KIEV, Ukraine -- Ukrainian President Petro Poroshenko ordered his forces to cease fire Friday and halt military operations for a week against pro-Russia separatists in the country's east -- the first step in a peace plan he hopes will end the conflict that has cost hundreds of lives.
The Kremlin dismissed the plan, saying it sounded like an ultimatum and lacked any firm offer to open talks with insurgents.
Poroshenko, speaking during his first trip as president to the troubled east, said troops still would fire back if separatists attacked them or civilians. He stressed the cease-fire was temporary and would end at 10 a.m. (0700GMT) on June 27.
"The Ukrainian army is ceasing fire," he said in a statement carried on his official website. "But this does not mean that we will not resist. In case of aggression toward our troops, we will do everything to defend the territory of our state."
Separatists in the Donetsk and Luhansk regions have declared independence from his government in Kiev, occupied public buildings and fought with heavy weapons against Ukrainian troops. Rebel leaders have already dismissed Poroshenko's plan and it remains to be seen to what extent they would comply -- or how much pressure Russia would put on them to cease fire as well.
Russia denies supporting the insurrection and has said that Russians fighting in Ukraine are doing so as private citizens.
The Kremlin said in a statement Friday that an initial analysis of Poroshenko's plan shows that "it's not an invitation for peace and talks, but an ultimatum" to insurgents in southeast Ukraine to lay down weapons. It said the plan "lacks the main element -- an offer to start talks."
The Kremlin said Poroshenko's government published his peace plan "deliberately or accidentally" at roughly the same moment that Ukrainian forces fired into Russian territory, wounding a Russian customs officer. It said the Russian side was waiting for Ukrainian "explanations and excuses" over the attack.
The Ukrainian Defense Ministry said that its forces were trying to flush out insurgents near the border checkpoint, but denied targeting it.
Leonid Slutsky, a senior lawmaker in the lower house of Russian parliament, said Putin could be waiting to see concrete actions by the Ukrainian forces to stop fighting.
"That will be a proof that Poroshenko is indeed the president. That could be considered the first step toward peace," Slutsky said, according to an ITAR-Tass report.
Russian President Vladimir Putin has criticized Ukraine's military operation against the rebels, but he has resisted the rebels' pleas to join Russia and related appeals from Russian nationalists for Putin to send troops into Ukraine.
The White House and European leaders urged support for the plan.
White House spokesman Josh Earnest said the U.S. government "has been very clear in our support for President Poroshenko's effort to bring peace and unity to Ukraine." He said the White House wanted Russia "to stop supporting the militants who are fomenting so much violence and instability."
Tension between Russia and Ukraine escalated sharply in February when protests in favor of closer ties with the European Union drove President Viktor Yanukovych from office. Russia denounced the events as an illegal coup involving radical nationalists and annexed the mostly Russian-speaking Crimea region. The rebellion in the eastern regions broke out shortly afterward, with Ukraine accusing Russia of supporting it.
Poroshenko's cease-fire order specified that Ukrainian forces would halt offensive operations at 10 p.m. (1900 GMT, 3 p.m. EDT).
The move is intended to give separatists time to lay down their arms and fighters from Russia safe passage to leave the country. Proposed next steps include joint security patrols to prevent crime and looting, new local and parliamentary elections, and measures to protect language rights of Russian speakers dominant in the east.
In the longer term, Poroshenko has suggested decentralizing political authority to the regions.
Poroshenko made his announcement while speaking with residents in the town of Sviatohirsk in Donetsk. It was his first visit as president to the east since his June 7 inauguration. Refugees from the rebel-held town of Slovyansk, where some of the worst fighting has taken place, attended the meeting.
Earlier Friday, at the border crossing near Izvaryne in the separatist Luhansk region, an AP reporter saw a line of 100 or more cars waiting for hours to cross from Ukraine into Russia as people fled the unrest. Some cars were piled high with possessions. The United Nations said earlier this week that 34,000 people had been displaced by the fighting.
One car had a sign saying "children" on the windshield. A man named Sergei, who would not give his last name for fear of retaliation, said, "People are simply leaving everything and trying to escape the war."
The United Nations says at least 356 people have been killed since May 7 and 34,000 have fled their homes. The U.N. report doesn't include casualties from previous weeks of fighting, so the actual death toll could be significantly higher.
Before the cease-fire announcement, Putin's foreign policy aide, Yuri Ushakov, said the Russian president is committed to dialogue on Ukraine and plans to talk soon by phone to U.S. President Barack Obama.
Ushakov said Putin, on a visit to Austria next week, would meet the chairman of the Organization for Security and Cooperation in Europe to discuss Poroshenko's peace plan.