Russian President Vladimir Putin and Ukrainian President Petro Poroshenko agreed Sunday to meet later this week to discuss a peace plan spearheaded by France and Germany.
The two leaders will meet in Minsk, Belarus, on Wednesday, along with French President François Hollande and German Chancellor Angela Merkel.
The four spoke by phone on Sunday to discuss the ongoing conflict in eastern Ukraine, which has killed more than 5,000 people.
Steffen Seibert, a spokesperson for the German Chancellor, described the call as "intensive."
However, Putin said the leaders still need to agree on "a number of points" before Wednesday, Agence France-Presse reported.
"We will be aiming for Wednesday, if by that time we manage to agree on a number of points which we've been intensely discussing lately," Putin told Belarus President Alexander Lukashenko in a meeting in the Russian resort town of Sochi.
A tentative ceasefire deal was previously struck in September in Minsk, but has since come undone due to renewed fighting.
Wednesday's meeting was agreed to after Merkel and Hollande spent the latter half of last week flying between Kiev and Moscow for talks on their new peace initiative.
"I think this is one of the last chances, that's why we took this initiative," Hollande told reporters on Saturday.
"If we don't manage to find not just a compromise but a lasting peace agreement, we know perfectly well what the scenario will be. It has a name. It's called war," he said.
Western nations accuse Moscow of propping up the pro-Russian separatists that have seized swathes of eastern Ukraine and declared autonomy.
The U.K. Foreign Secretary Philip Hammond told Britain's Sky News on Sunday that Putin had been behaving like a "mid-20th century tyrant."
"This man has sent troops across an international border and occupied another country's territory in the 21st century acting like some mid-20th century tyrant. Civilised nations do not behave like that," Hammond said.
"We do not see any reason to tolerate this kind of outrageous and outdated behaviour from the Kremlin."