Turkey's Presidential Spokesman Ibrahim Kalin and U.S. National Security Advisor H.R. McMaster held a meeting on Sunday in Istanbul.

They discussed several issues, including the long-term strategic partnership between the two countries, according to presidential sources who asked not to be named due to restriction on speaking to the media.

They exchanged views on regional developments and mutual strategic challenges.

Also, ways to develop a joint fight against all kinds of terrorism were discussed in detail.

Turkey-U.S. relations have been strained recently following America’s backing and arming of PYD/PKK terror group in Syria.

More than 1,200 people, including security force personnel and civilians, have lost their lives since the PKK -- listed as a terrorist organization by Turkey, the U.S., and EU -- resumed its decades-old armed campaign in July 2015.