Moscow believes Turkish President Recep Tayyip Erdogan will "officially" offer at an upcoming meeting with Russian leader Vladimir Putin in Kazakhstan to mediate negotiations with Ukraine, a Kremlin aide said Wednesday.

"The Turks are offering their mediation. If any talks take place, then most likely they will be on their territory: in Istanbul or Ankara," Kremlin foreign policy advisor Yuri Ushakov told reporters in Moscow.

He added that "Erdogan will probably propose something officially" during talks with Putin in the Kazakh capital Astana on Thursday.

NATO member Turkey, which has stayed neutral throughout the conflict in Ukraine, has good relations with its two Black Sea neighbours -- Russia and Ukraine, and has refrained from joining Western sanctions on Moscow.

"Turkey on principle does not join the illegal sanctions of the West. And this position of Turkey gives an additional impetus for the expansion of trade and economic cooperation," Ushakov said.

Turkey has twice hosted talks between Moscow and Kyiv, including a March in-person meeting of Russia's Foreign Minister Sergei Lavrov and his Ukrainian counterpart Dmytro Kuleba, the first high-level talks to take place after Moscow sent troops into Ukraine.

However, peace negotiations have since stalled and Ukraine's President Volodymyr Zelensky said he will not hold any talks with Putin after the Kremlin claimed to have annexed four territories of Ukraine.

Asked about Zelensky's pledge, Ushakov told reporters: "I would like to tell him: never say never".

Turkey and the United Nations had brokered a landmark deal with Moscow and Kyiv that designated three ports for Ukraine to send much-needed grain supplies through a Russian blockade.

But Russia has criticised the deal, complaining its own exports had suffered and claiming without evidence that most deliveries were arriving to Europe, not in poor countries where grain was needed most.

Turkey also played a key role in one of the largest prisoner swaps between Russia and Ukraine since the start of Moscow's military campaign, in which over 200 prisoners were released.

Erdogan is keen to boost trade with Moscow as he tries to stabilise the battered Turkish economy in the run up to elections next June.

Ahead of their meeting, Putin proposed the creation of an energy hub in Turkey after several leaks were discovered on the Nord Stream gas pipelines to Europe.

Russia could "move to the Black Sea region... its main route for the supply of fuel and gas to Europe through Turkey, creating the largest gas hub in Turkey", Putin said at an energy forum in Moscow.