ANKARA - Top advisers for Turkey’s President Recep Tayyip Erdogan and US President Joe Biden spoke on the phone on Tuesday, marking the first official contact between the two countries since Biden took office nearly two weeks ago.

Erdogan’s Chief Foreign Policy Adviser Ibrahim Kalin and US national security adviser Jake Sullivan discussed issues regarding Syria, Libya, the eastern Mediterranean, Cyprus, and Nagorno-Karabakh, Turkey’s official news agency Anadolu reported

Erdogan’s Chief Foreign Policy Adviser Ibrahim Kalin and US national security adviser Jake Sullivan discussed issues regarding Syria, Libya, the eastern Mediterranean, Cyprus, and Nagorno-Karabakh, Turkey’s official news agency Anadolu reported.

Kalin told Sullivan that joint efforts were needed to find a solution to current disagreements between the countries, such as Turkey’s purchase of Russian S-400 defense systems and US support for Kurdish militia groups in northern Syria, Anadolu said.

In its statement on the meeting, the White House said Sullivan underscored the Biden administration’s desire to build “constructive” US-Turkey ties but also touched on areas of friction.

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Sullivan “conveyed the administration’s intention to strengthen transatlantic security through NATO, expressing concern that Turkey’s acquisition of the Russian S-400 surface-to-air missile system undermines alliance cohesion and effectiveness,” National Security Council spokeswoman Emily Horne said.

NATO allies Washington and Ankara have been at loggerheads over Turkey’s purchase of the Russian-made D-400 defense systems. In December, the Trump administration imposed long-anticipated sanctions on Turkey over the acquisition, a move Turkey called a “grave mistake.”

It had also removed Turkey, a NATO ally, from its F-35 fighter jet program as a result.

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Washington says the S-400s pose a threat to its advanced F-35 fighters and to NATO’s broader defense systems. Turkey rejects this, saying the S-400s will not be integrated into NATO, and has offered to form a joint working group to examine the conflicting claims.

Ankara says its purchase of the S-400s was not a choice, but rather a necessity because it was unable to procure missile defenses from other NATO allies with satisfactory conditions.