Turkish President Recep Tayyip Erdogan held phone talks with Ukrainian President Volodymyr Zelenskyy on Saturday.

In a statement, the Turkish presidency says Ankara is making efforts for an immediate ceasefire between Russia and Ukraine. It said Erdogan expressed condolences for Ukrainians killed in the Russian operation.

After the phone call, Zelenskyy said Turkey has banned the passage of Russian warships to the Black Sea and tweeted gratitude for Turkish support. "The ban on the passage of Russian warships to the Black Sea and significant military and humanitarian support for Ukraine are extremely important today," he wrote. 

But Turkish media said that Turkey has not yet made a decision to close the straits to Russian ships, citing an unnamed Turkish senior official.

Turkish foreign minister on Thursday said they cannot stop Russian warships accessing the Black Sea via its straits, as Ukraine had requested, citing a clause in an international pact.

Meanwhile, TASS reported that Turkish Foreign Minister Mevlut Cavusoglu and his Russian counterpart Sergey Lavrov also held talks by phone on Saturday and touched upon the latest developments in Ukraine.

The report said Cavusoglu warned against further escalating military tensions and expressed Turkey's readiness to hold talks between Russia and Ukraine if the parties were willing to do so. Belarus and Hungary have also made similar proposals.

The Kremlin on Saturday said that Kyiv has refused to begin talks. Ukraine has denied the claim.

Mykhailo Podolyak, an adviser to the office of Zelenskyy, told Reuters that his country has prepared a negotiating position but was faced with impractical negotiating conditions from Russia.

(With input from agencies)