Russian President Vladimir Putin, left, and Turkish President Recep Tayyip Erdogan shake hands during their meeting in the Kremlin in Moscow, Russia, Monday, April 8, 2019. The talks are expected to focus on the situation in Syria, where the two countries have closely coordinated their steps. (Alexei Nikolsky, Sputnik, Kremlin Pool Photo via AP)

MOSCOW (AP) — Russian President Vladimir Putin hosted his Turkish counterpart in Moscow on Monday, discussing how to coordinate their next moves in Syria and how to deepen business ties, including the sale of advanced Russian missiles to Turkey that has riled the United States.

Turkish President Recep Tayyip Erdogan's visit to Russia, his third this year, underlined the increasingly close cooperation between the two countries and Turkey's readiness to defy the U.S.

Last week, U.S. Vice President Mike Pence warned Turkey that it was risking its NATO membership and its participation in the F-35 fighter program by failing to heed Washington's demand to cancel the contract with Russia for the S-400 air defense missile systems.

After Monday's talks, Erdogan said that Turkey considers the Russian deal done and won't submit to pressure.

"On the issue of the S-400s, we have determined our road map, we have taken steps," Erdogan said. "Those who tell us to give up our plans, those who make recommendations do not know us. If we have made a contract, if we have reached a deal, then this business is finished. This is our sovereign right, this is our decision."

Putin described the S-400 contract as a top priority in cooperation between the two countries, adding that other weapons deals are in the making.

"We may reach agreements on the joint development and production of high-tech weapons," he said.

Turkey's purchase of the Russian missiles marked the first such contract for a NATO member. Turkey has ignored U.S. demands to abandon the agreement, and Erdogan said Friday that deliveries of the S-400s will begin in July.

The Turkish leader noted that Washington had offered Ankara the U.S.-made Patriot air defense system, but said the U.S. offer isn't as favorable as Russia's.

The U.S. and other NATO allies say the S-400s aren't compatible with the alliance's weapons systems. Washington has voiced concerns that their use by Turkey could compromise security of the state-of-the art U.S. F-35 fighter jets that Turkey stands to receive.

Putin and Erdogan also talked about the completion of a pipeline that will carry Russian gas to Turkey, the planned construction of Turkey's first nuclear power plant, which is to start operations in 2023, and other economic projects.

Erdogan said the number of Russian tourists who visited Turkey last year reached a record 6 million.

Putin and Erdogan have developed a close personal rapport and held regular meetings. They called each other "my dear friend" throughout the talks, saying that the two countries plan to expand their annual trade, currently at about $25 billion, to $100 billion.

Putin said the construction of the underwater segment of the Turkish Stream gas pipeline crossing the Black Sea has just been completed, adding that it's set to come online later this year.

On Syria, Russia and Iran have thrown their support behind Syrian President Bashar Assad, while Turkey has backed his foes during the eight-year war. Despite that, the three countries have teamed up to broker a peace deal for Syria, united by their shared desire to undercut U.S. clout in the region.

Russia and Turkey also have closely coordinated moves on Syria, where they struck a deal in September to create a security zone in the northern province of Idlib. That agreement averted a Syrian army offensive that had sparked fears of a humanitarian catastrophe.

Putin said Russia and Turkey so far have failed to fully implement September's agreement, but emphasized that significant progress has been made.

"We have moved forward, albeit not as quickly as we hoped," he said.

Erdogan also voiced support for the deal in Syria.

"We have taken the steps we need to take and we will continue to do so," Erdogan said. "There is no turning back."

The Turkish leader emphasized Ankara's intention to create a safe zone to keep the Syrian Kurdish militia — the People's Protection Units, or YPG — away from its border. Turkey views YPG as a "terrorist group" for its ties to outlawed Kurdish rebels inside Turkey.

"We have said that we will not agree to a structure in Syria's north that would threaten our security as well as Syria's territorial integrity," Erdogan said.

Putin and Erdogan vowed to continue efforts to encourage political settlement in Syria by pushing for the creation of a committee to draft the country's new constitution.

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Fraser reported from Ankara.

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A previous version of this story has corrected the spelling of the Syrian province to Idlib, not Ildib.

Russia's President Vladimir Putin, left, walks to shake hands with Turkey's President Recep Tayyip Erdogan, right, as he welcomes him prior to their meeting in Moscow, Russia, Monday, April 8, 2019. Russian President Vladimir Putin is hosting his Turkish counterpart, Recep Tayyip Erdogan, for talks expected to focus on the situation in Syria and their two nations' booming economic ties. (Presidential Press Service via AP, Pool)
Turkish President Recep Tayyip Erdogan enters a hall for his talks with Russian President Vladimir Putin in the Kremlin in Moscow, Russia, Monday, April 8, 2019. The talks are expected to focus on the situation in Syria, where the two countries have closely coordinated their steps. (Alexei Nikolsky, Sputnik, Kremlin Pool Photo via AP)
Turkish President Recep Tayyip Erdogan, left, and Russian President Vladimir Putin arrive for a meeting with businessmen in the Kremlin in Moscow, Russia, Monday, April 8, 2019. Russian President Vladimir Putin on Monday hosted Turkish counterpart Recep Tayyip Erdogan for talks focusing on the situation in Syria, the sale of advanced Russian missiles to Turkey and other economic deals. (Maxim Shipenkov/Pool Photo via AP)
Russian President Vladimir Putin, left, shakes hands with Turkish President Recep Tayyip Erdogan during their meeting in the Kremlin in Moscow, Russia, Monday, April 8, 2019. Russian President Vladimir Putin is hosting his Turkish counterpart, Recep Tayyip Erdogan, for talks expected to focus on the situation in Syria and their two nations' booming economic ties. (Maxim Shipenkov/Pool Photo via AP)
Russian President Vladimir Putin, right, listens to Turkish President Recep Tayyip Erdogan during their meeting in the Kremlin in Moscow, Russia, Monday, April 8, 2019. The talks are expected to focus on the situation in Syria, where the two countries have closely coordinated their steps. (Alexei Nikolsky, Sputnik, Kremlin Pool Photo via AP)
Russian President Vladimir Putin, right, speaks with Turkish President Recep Tayyip Erdogan during their meeting in the Kremlin in Moscow, Russia, Monday, April 8, 2019. Russian President Vladimir Putin is hosting his Turkish counterpart, Recep Tayyip Erdogan, for talks expected to focus on the situation in Syria and their two nations' booming economic ties. (Maxim Shipenkov/Pool Photo via AP)
Russia's President Vladimir Putin, left, shakes hands with Turkey's President Recep Tayyip Erdogan as he welcomes him prior to their meeting in Moscow, Russia, Monday, April 8, 2019. Russian President Vladimir Putin is hosting his Turkish counterpart, Recep Tayyip Erdogan, for talks expected to focus on the situation in Syria and their two nations' booming economic ties. (Presidential Press Service via AP, Pool)
Turkish President Recep Tayyip Erdogan, left, and Russian President Vladimir Putin attend a meeting with businessmen in the Kremlin in Moscow, Russia, Monday, April 8, 2019. Russian President Vladimir Putin on Monday hosted Turkish counterpart Recep Tayyip Erdogan for talks focusing on the situation in Syria, the sale of advanced Russian missiles to Turkey and other economic deals. (Maxim Shipenkov/Pool Photo via AP)
Russian President Vladimir Putin, right, shakes hands with Turkish President Recep Tayyip Erdogan after a joint news conference following their talks in the Kremlin in Moscow, Russia, Monday, April 8, 2019. The talks are expected to focus on the situation in Syria, where the two countries have closely coordinated their steps. (AP Photo/Alexander Zemlianichenko)
Russian President Vladimir Putin, right, and Turkish President Recep Tayyip Erdogan leave a joint news conference following their talks in the Kremlin in Moscow, Russia, Monday, April 8, 2019. The talks are expected to focus on the situation in Syria, where the two countries have closely coordinated their steps. (AP Photo/Alexander Zemlianichenko)
Russian President Vladimir Putin, right, and Turkish President Recep Tayyip Erdogan pose for a photo after a joint news conference following their talks in the Kremlin in Moscow, Russia, Monday, April 8, 2019. The talks are expected to focus on the situation in Syria, where the two countries have closely coordinated their steps. (AP Photo/Alexander Zemlianichenko)
Russian President Vladimir Putin, right, gestures during his and Turkish President Recep Tayyip Erdogan joint news conference following their talks in the Kremlin in Moscow, Russia, Monday, April 8, 2019. The talks are expected to focus on the situation in Syria, where the two countries have closely coordinated their steps. (AP Photo/Alexander Zemlianichenko)