KIEV, Ukraine -- Ukrainian President Petro Poroshenko tried to keep his peace plan to settle the conflict with pro-Russian separatists on track in a four-way phone call Sunday with Russian President Vladimir Putin and the leaders of France and Germany.
The two-hour conversation came ahead of a Monday deadline that European Union leaders set for Russia and the separatists to take steps to ease the violence, warning that otherwise they were ready "at any time" to impose further punitive measures.
German Chancellor Angela Merkel and French President Francois Hollande encouraged the Ukrainian and Russian presidents to work on meeting the EU conditions, Hollande's office said in a statement. The EU's demands included the return of three border checkpoints to Ukrainian control, verification of the cease-fire by monitors from the Organization for Security and Cooperation in Europe, and talks to put Poroshenko's peace plan in place.
The call was the latest in a series of discussions the four leaders have held in recent weeks in an effort to stop the fighting that has killed more than 400 people since April. A cease-fire in place since June 20 has been shaky, with each side accusing the other of numerous violations.
A statement issued by Poroshenko's office said he underlined Ukraine's willingness to maintain the cease-fire at least until Monday evening, but expressed concern about the situation, noting what he said were multiple violations of the truce by separatist fighters. He called on Putin to strengthen border controls from the Russian side to stop what Ukraine says is the flow of weapons, fighters and mercenaries.
The sides agreed that more talks among representatives of Ukraine, Russia and the separatists would convene "very soon," Poroshenko's office said.
A Kremlin statement said the four leaders discussed having OSCE monitors stationed at the border crossing points. They also discussed issues resulting from Ukraine's signing of a broad trade deal with the EU on Friday despite Russia's objections. Russian officials have said Ukraine's tariff-free trade arrangement with Russia may be withdrawn, but no trade sanctions have yet been announced.
In another indication that tensions remain high, several hundred Ukrainian soldiers and activists gathered outside the presidential administration in Kiev on Sunday to demand that Poroshenko lift the cease-fire and allow them to resume their fight.
A presidential administration official, Henadiy Zubko, promised to pass on their demands to the president, but told them that the cease-fire order would remain in effect until 10 p.m. Monday (1900GMT).
Soldiers also addressed several thousand people who turned out for the traditional Sunday rally on Independence Square in central Kiev.
Another EU condition was fulfilled late Saturday, when pro-Russia separatists released a second team of four OSCE observers who had been held captive in eastern Ukraine since the end of May. The first team of four was freed last week.
The free-trade pact that Ukraine signed with the EU was the very deal that the former Ukrainian president dumped under pressure from Moscow in November, fueling huge protests that eventually drove him from power. Moscow responded to those events by annexing the mainly Russian-speaking Crimean Peninsula in March, and the pro-Russia insurgency in eastern Ukraine broke out a month later.
The United States and the EU have slapped travel bans and asset freezes on members of Putin's inner circle, and threatened to impose more crippling sanctions against entire sectors of Russia's economy if the Kremlin fails to de-escalate the crisis.