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".

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

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.