In a four-way phone conversation involving leaders from Russia, Ukraine, Germany and France, Ukraine's Petro Poroshenko called for Russian president Vladimir Putin to halt arms supplies to rebels.
The Ukrainian president also insisted there be a deployment of United Nations peacekeepers to conflict areas near the Russian border. The four countries vowed to implement a peace plan brokered in Monday's phone call.
France, Germany and Russia have mediated talks between Ukraine and Russian-aligned rebels who have been fighting since April 2014 in a conflict that has taken 10,000 lives. The conflict has worsened recently – More than 20 Ukrainian military personnel have been reported killed in the last four weeks.
Poroshenko has described the fighting in the last days of July as the bloodiest this year. A statement released by his presidency after the talks, Poroshenko said he urged Russia "to immediately cease aggressive actions and supply of weapons to the occupied territories."
Last week, rebel chief Alexander Zakharchenko said he wanted to establish a new state called Malorossiya, or "Little Russia." The separatists aspire to include in that designation not only the area they currently control in eastern Ukraine but territory beyond that.
France president Emmanuel Macron, participating in this mediation for the first time since being elected, and Germany president Angela Merkel have rejected the idea of a rebel state, Poroshenko's office said.
Macron, Merkel and Putin discussed the conflict earlier this month while in Hamburg for the G20 summit. Merkel described the meeting as "very, very slow" progress towards resolving the conflict in Ukraine.
dv/kl (AP, AFP, dpa)