Ukraine said Sunday it destroyed Russian bombers worth billions of dollars in a "large-scale" drone assault on enemy soil as it geared up for talks with Moscow counterparts to explore prospects for a ceasefire.

Ukraine claimed it damaged US$7 billion worth of Russian aircraft parked at four airbases thousands of kilometres away, with unverified video footage showing aircraft engulfed in flames and black smoke.

A source in the Ukrainian security services said the drones were concealed in the ceilings of shipping containers which were opened up to release them for the assault.

Ukraine's President Volodymyr Zelensky said 117 drones were deployed in what he called "our most long-range operation" in more than three years of war.

"Thirty-four percent of the strategic cruise missile carriers at the airfields were hit," he said.

Meanwhile, he said on a Ukrainian delegation to Istanbul is led by his defence minister Rustem Umerov for talks on Monday with Russian officials.

Zelensky said he had defined the Ukrainian delegation's position going into it, with priorities included "a complete and unconditional ceasefire" and the return of prisoners and abducted children.

The Russian delegation, headed by Vladimir Medinsky, has arrived in Turkey for the second round of peace talks.

Russia said it has formulated its own peace terms but refused to divulge them in advance. (AFP)