Two U.S. senators are warning that Russian President Vladimir Putin is stalling on peace while preparing a fresh military offensive against Ukraine.

The latest suspected attack is a serious blow to Putin's nuclear dominance but it comes amid one of Russia's biggest attacks of the last three years

The drone attacks came on the eve of expected peace talks in Istanbul between Russia and Ukraine, which were already strained by uncertainty and pressure from U.S. President Donald Trump.

Trump previously said his personal relationship with Putin would usher in peace for Ukraine. Now, he says Putin's gone "absolutely CRAZY!"

Russian President Vladimir Putin’s conditions for ending the war in Ukraine include a demand that Western leaders pledge in writing to stop enlarging NATO eastwards, according to reports.

The U.S. president lashed out at the Kremlin on Tuesday as the White House continued to consider increasing sanctions against Russia.

Dozens of Russian military aircraft have been destroyed in an unprecedented drone attack deep inside Russia, a Ukrainian official has said, the day before critical peace talks between Moscow and Kyiv resume in Istanbul.