The Russian president met with his Turkish counterpart Recep Tayyip Erdogan on Monday, who arrived in Moscow for talks about the state of Russian-Turkish relations.

Russia and Turkey have other arms sales projects in the works apart from the S-400 air defence system deal, Russian President Vladimir Putin said, speaking at the opening of a meeting of the Russian-Turkish Cooperation Council on Monday.

Putin stressed that the completion of the $2.5 billion contract to deliver Russian-made S-400s to Turkey is presently the top priority when it comes to military-technical cooperation between the two countries.

"There are serious tasks facing our countries when it comes to strengthening cooperation in the military-technical sphere. First and foremost, we are talking about the completion of the contract to supply Turkey with the Triumf S-400 anti-aircraft missile systems," Putin said.

"There are other promising projects on the agenda related to the supply of modern Russian defence products to Turkey," Putin added, without specifying what these might be.

Speaking to reporters at a press conference following his talks with Erdogan, Putin noted that Moscow and Ankara may very well reach agreements on the joint development and production of "modern, high-tech military equipment" at some point in the future.

For his part, President Erdogan stressed that Turkey's decision to buy the Russian-made S-400 was the country's "sovereign right," adding that no one had a right to demand that Ankara abandon its deal with Moscow. Erdogan reiterated his position that the S-400 question was "closed."

Moscow and Ankara penned a $2.5 billion contract on the supply of four battalion sets-worth of Russian-made S-400s to Turkey in late 2017. Once deliveries begin in July, Turkey will become just the fourth country to possess the system after Russia itself, Belarus and China. Designed to stop enemy aircraft, drones, cruise and ballistic missiles, the S-400 is presently the most advanced mobile air defence system in Russia's arsenal. Last month, Turkish media indicated that the first of Turkey's S-400s would be deployed to the Murted Air Base northwest of Ankara.

Last week, Putin said that S-400 manufacturer Almaz-Antey had accelerated the production of the Turkey-bound S-400s at Ankara's request.

The S-400 contract has emerged as a major headache for Washington and US arms manufacturers, who offered to sell Turkey the Patriot PAC-3 air defence system in place of the S-400. US officials have threatened to block deliveries of Lockheed Martin's F-35 new fifth-generation stealth fighter to Ankara if it goes through with the S-400 purchase amid fears that the Russian air defence system could compromise the F-35's stealth capabilities.

Putin hosted his Turkish counterpart Recep Tayyip Erdogan on Monday for talks on a range of issues, including the situation in Syria, economic ties, and energy cooperation. Before taking off for Moscow on Monday, Erdogan told Turkish media that Ankara was "ready" to launch a new operation in northern Syria against US-backed Kurdish militia which Turkey classifies as terrorists.