Ukraine said it had begun "hard" talks on a ceasefire, immediate withdrawal of troops and security guarantees with Russia on Monday, raising tentative hopes for an end to the conflict that has killed thousands.

Both sides reported rare progress during the weekend after earlier rounds of negotiations have primarily focused on ceasefires to get aid to towns and cities under siege by Russian forces and evacuate civilians; those truces have frequently failed.

Posting online ahead of the talks, Ukrainian negotiator Mykhailo Podolyak wrote: "Russia is already beginning to talk constructively... I think that we will achieve some results literally in a matter of days." He later said discussions had started but were hard because the political systems of Russia and Ukraine were too different.

Podolyak said he believed Russia "still has a delusion that 19 days of violence against (Ukrainian) peaceful cities is the right strategy."

Russia says it was forced to launch the military operation because its security demands were not met as NATO continued its eastward expansion.

(With input from Reuters)