Ukraine will make securing a ceasefire a priority in expected talks with a Russian delegation in Istanbul on Friday, a Ukrainian diplomatic source said, adding there was also a need for "confidence-building measures".

Direct peace talks between Russia and Ukraine are expected, with lower-level delegations. This will be the first time the two countries have held direct talks since the first weeks of Russia's invasion.

Russia resumed mass drone attacks in Ukraine early on Sunday, after its self-declared three-day pause expired.