Turkish President Recep Tayyip Erdogan is due to meet in Moscow with Russian President Vladimir Putin on April 8.
His visit comes just days after a dispute between Washington and Ankara intensified over Turkey's possible military plans in Syria and its purchase of a Russian-built surface-to-air missile system.
Turkey is a member of NATO and its relations with Russia have historically been tense.
But Moscow and Ankara have established strong economic ties since the end of the Cold War and have moved closer in recent years as Turkey's relations with Washington and the European Union have suffered.
Meanwhile, the United States and other NATO countries are at loggerheads with Turkey over its decision to purchase a Russian S-400 air-defense system that is not compatible with NATO systems and is seen as a threat to U.S.-made F-35 fighter jets.
Washington has demanded that Ankara call off its deal with Russia and has suspended Turkey's participation in the F-35 program..
U.S. Vice President Mike Pence said on April 3 that "Turkey must choose” whether it wants to "remain a critical partner" in NATO or "risk the security of that partnership by making such reckless decisions that undermine our alliance."
The U.S. State Department said last week that Ankara could face U.S. sanctions if it goes ahead with the purchase.
Turkish Foreign Minister Melvut Cavusoglu, who was in Washington to mark NATO's 70th anniversary, told US. public television on April 4 that it was "unacceptable" for Washington to refuse to sell weapons to Turkey and also insist that Ankara cannot buy a defense system from another country.
Cavusoglu, who has said "the S-400 deal is a done deal" that Ankara will not step back from, suggested a working group be formed between the Pentagon and Ankara to address the dispute.
But the Pentagon rejected that proposal, saying that a "technical working group at this stage is not necessary or a path the United States is considering as a resolution."
The U.S. State Department says Secretary of State Mike Pompeo last week also warned Cavusoglu of "potentially devastating consequences" if Turkey were to launch an offensive against U.S.-backed Kurdish forces in Syria.
The United States and Turkey support differing antigovernment rebels in Syria's eight-year civil war.
The U.S. military has been backing Syrian Kurdish fighters in the north of the country in their battle against Islamic State (IS) extremists. Ankara considers the Kurds to be terrorists with ties to Kurdish separatists operating in Turkey and has vowed to wipe them out.
Russia supports the forces of Syrian President Bashar al-Assad’s government.
