SHANGHAI (AP) — New York University said Monday it was seeking more information from Chinese authorities after nine students from its Shanghai campus were temporarily detained in what appeared to be police dragnet for drug suspects.

A statement from the university said two students were held as part of a police action outside a bar and the other seven were at a birthday party at an off-campus apartment on March 12 when police arrived and brought all present in for drug testing.

“None of the students were found to have used or been in possession of drugs and none were arrested,” NYU Shanghai said in a statement. China hosts a large number of foreign students, a number increased by the opening of satellite campuses by British and American universities.

“Being brought in for testing as part of a drug sweep was understandably frightening for our students ... Since then we have continued to provide support for the affected students," said a statement from the school sent to The Associated Press on Monday.

Police who arrived at the birthday party were apparently looking for a specific individual but it wasn’t clear who that was and no one was arrested.

The students at the bar that same night told school authorities that, upon leaving the venue, they were approached by a person wearing plainclothes who showed a badge they did not recognize. One tried to leave, both were detained and suffered minor injuries, and all other bar patrons and staff, all of them Chinese citizens, were also detained and subjected to drug testing.

The students, who were not identified by name or nationality, were all released by the next morning after their drug tests came back negative, NYU said.

“We are currently seeking more information from city authorities to better understand last weekend’s police actions," the university's statement said.

There was no immediate response to requests for comment from the Shanghai police. People caught using recreational drugs such as marijuana and cocaine can be locked up for months or longer in China, while dealers can receive the death sentence.