Court artist sketch by Elizabeth Cook shows lorry driver Maurice Robinson, 25, on a video-link at Chelmsford Magistrates' Court, England, Monday Oct. 28, 2019. Authorities found 39 people dead in a truck in an industrial park in England on Wednesday and arrested the driver on suspicion of murder in one of Britain's worst human-smuggling tragedies. (Elizabeth Cook/PA via AP)

LONDON (AP) — British Prime Minister Boris Johnson on Monday honored the 39 victims who died in a container as the truck driver made his first court appearance after being charged with manslaughter and conspiracy.

Johnson and Home Secretary Priti Patel traveled to the site in southeastern England to sign a condolence book and place a wreath in remembrance of the victims, whose identities and origins are still shrouded in mystery.

"We mourn those who lost their lives," Johnson wrote. "Our thoughts are with their families far away. In condemning the callousness of those responsible for this crime, we in the government of the United Kingdom resolve to do everything in our power to bring the perpetrators to justice."

He said the tragedy had shocked Britain and the world, praising the victims as innocent people seeking better lives.

British officials initially said the eight women and 31 men who were found in a refrigerated truck container in an industrial park Wednesday, were from China, but it now appears at least some were from Vietnam.

Patel told Parliament on Monday that the nationalities of the victims "are not confirmed at this stage."

She said U.K. border officials would increase operations in Purfleet, the English port where the container arrived, and that Belgium has agreed to allow Britain to send more immigration officers to Zeebrugge, the Belgian port also used by the traffickers.

The truck driver, Maurice Robinson, appeared in Chelmsford Magistrates Court on Monday via video link from prison, but wasn't required to plead innocent or guilty.

The 25-year-old from Northern Ireland will be kept in custody until he appears at the Old Bailey court on Nov. 25, where he will be expected to enter a plea.

He is charged with 39 counts of manslaughter, two counts of conspiracy to facilitate human trafficking and other crimes.

His lawyer didn't request that Robinson be freed on bail.

Four other people have been arrested but not charged, including one in Ireland who remains in custody. The other three have been freed on bail while under investigation.

British officials face a huge task trying to identify the victims, who have been removed from the container in preparation for autopsies.

Most of their authentic documents had been seized by the traffickers, making identification much more difficult.

British authorities Monday gave Vietnam documents on four of the victims to help determine if they are from that country.

The papers were handed over to Vietnam's Ministry of Public Security and will be used to help identify the victims, Deputy Foreign Minister Pham Thanh Son was cited by the VNExpress news website as saying.

It wasn't immediately clear what type of documents were sent.

The tragedy has hit Vietnam directly despite initial reports of a Chinese connection. Up to 24 Vietnamese families have since reported missing relatives whom they fear to be among the dead.

Vietnamese authorities have taken hair and other forensic samples from families who have reported missing people to assist the identification efforts. They may prove vital as Britain tries to identify people without documents.

Smugglers normally take the passports of their passengers to obscure their identities, stripping them of their names and giving them new documents when they arrive at their destinations.

Families in central Vietnam continue to cling to hope that their missing loved ones aren't among the victims.

In Dien Thinh village in Nghe An province, Hoang Thi Ai cried Monday as she received relatives and neighbors coming to her house to check on the latest news on her missing 18-year-old son, Hoang Van Tiep, who the family fears may be among the victims.

Tiep worked as a restaurant dishwasher in France for two years before deciding to go to England for a better-paying job at a nail salon, Ai said.

Chinese Foreign Ministry spokesman Geng Shuang said China has asked British authorities to provide more information on the identity of the victims in what British officials have called one of the country's deadliest cases of human smuggling.

Geng also said Monday that reports that the victims had Chinese passports was "speculation."

Chinese Assistant Foreign Minister Chen Xiaodong said the case shows that illegal immigration is a global issue.

"It needs to be jointly dealt with and properly resolved by all parties concerned so that we can prevent a tragedy like this from repeating in the future," Chen said at a news conference in Beijing.

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Hau Dinh reported from Dien Thinh, Vietnam. Yanan Wang in Beijing contributed to this report.

Britain's Prime Minister Boris Johnson stands with the Chief Constable of Essex Police, Ben-Julian Harrington after laying flowers during a visit to Thurrock Council Offices, England, Monday Oct. 28, 2019. British police say they have arrested a fourth person in connection with the deaths of 39 people found in a truck in southeast England in one of Britain's worst human-smuggling tragedies. (Stefan Rousseau/Pool via AP)
Britain's Prime Minister Boris Johnson signs a book of condolence during a visit to Thurrock Council Offices, England, Monday Oct. 28, 2019. British police say they have arrested a fourth person in connection with the deaths of 39 people found in a truck in southeast England in one of Britain's worst human-smuggling tragedies. (Stefan Rousseau/Pool via AP)
Hoang Thi Ai holds up her phone showing a photo of her son Hoang Van Tiep, who she fears is one of the possible victims in the truck deaths in England, at her home in Dien Chau district, Nghe An province, Vietnam on Monday, Oct. 28, 2019. Families in central Vietnam continue to cling on hope for the fates of their loved ones, who might be among the dead in a truck in southern England. (AP Photo/Hau Dinh)
Britain's Prime Minister Boris Johnson walks with the Chief Constable of Essex Police, Ben-Julian Harrington, to lay flowers during a visit to Thurrock Council Offices, England, Monday Oct. 28, 2019. British police say they have arrested a fourth person in connection with the deaths of 39 people found in a truck in southeast England in one of Britain's worst human-smuggling tragedies. (Stefan Rousseau/Pool via AP)
Hoang Thi Ai, the mother of Hoang Van Tiep, one of the possible victims in the truck deaths in England, talks to a relative on phone at her home in Dien Chau district, Nghe An province, Vietnam on Monday, Oct. 28, 2019. Families in central Vietnam continue to cling on hope for the fates of their loved ones, who might be among the dead in a truck in southern England. (AP Photo/Hau Dinh)
Court artist sketch by Elizabeth Cook shows lorry driver Maurice Robinson, 25, on a video-link at Chelmsford Magistrates' Court, England, Monday Oct. 28, 2019. Authorities found 39 people dead in a truck in an industrial park in England on Wednesday and arrested the driver on suspicion of murder in one of Britain's worst human-smuggling tragedies. (Elizabeth Cook/PA via AP)
Hoang Thi Ai, the mother of Hoang Van Tiep, one of the possible victims in the truck deaths in England, stares off at her home in Dien Chau district, Nghe An province, Vietnam on Monday, Oct. 28, 2019. Families in central Vietnam continue to cling on hope for the fates of their loved ones, who might be among the dead in a truck in southern England. (AP Photo/Hau Dinh)
Hoang Thi Ai, mother of Hoang Van Tiep, left, one of the possible victims in the truck deaths in England, talks on the phone with a relative as her daughter Hoang Thi Nhiem holding her son at her home in Dien Chau district, Nghe An province, Vietnam on Monday, Oct. 28, 2019 . Families in central Vietnam continue to cling on hope for the fates of their loved ones, who might be among the dead in a truck in southern England. (AP Photo/Hau Dinh)
A man rides his bicycle past a Catholic church in the Dien Thinh village, Nghe An province, Vietnam on Monday, Oct. 28, 2019 . Families in central Vietnam continue to cling on hope for the fates of their loved ones, who might be among the dead in a truck in southern England. (AP Photo/Hau Dinh)
Nguyen Thanh Le holds his phone showing a photo of his son Nguyen Van Hung on Monday, Oct. 28, 2019 in Dien Chau district, Nghe An province, Vietnam. Families in central Vietnam continue to cling on hope for the fates of their loved ones, who might be among the dead in a truck in southern England. (AP Photo/Hau Dinh)
Nguyen Thanh Le holds up his phone showing a photo of his son Nguyen Van Hung on Monday, Oct. 28, 2019, in Dien Chau district, Nghe An province, Vietnam. Families in central Vietnam continue to cling on hope for the fates of their loved ones who might be among the dead in a truck in southern England. (AP Photo/Hau Dinh)
Britain's Prime Minister Boris Johnson lays flowers during a visit to Thurrock Council Offices, England, Monday Oct. 28, 2019. British police say they have arrested a fourth person in connection with the deaths of 39 people found in a truck in southeast England in one of Britain's worst human-smuggling tragedies. (Stefan Rousseau/Pool via AP)
Britain's Prime Minister Boris Johnson stands with the Chief Constable of Essex Police, Ben-Julian Harrington and Home Secretary Priti Patel, after laying flowers during a visit to Thurrock Council Offices, England, Monday Oct. 28, 2019. British police say they have arrested a fourth person in connection with the deaths of 39 people found in a truck in southeast England in one of Britain's worst human-smuggling tragedies. (Stefan Rousseau/Pool via AP)
Court artist sketch by Elizabeth Cook shows lorry driver Maurice Robinson, 25, on a video-link at Chelmsford Magistrates' Court, England, Monday Oct. 28, 2019. Authorities found 39 people dead in a truck in an industrial park in England on Wednesday and arrested the driver on suspicion of murder in one of Britain's worst human-smuggling tragedies. (Elizabeth Cook/PA via AP)