KIEV, Ukraine — Rebels killed five Ukrainian soldiers in violation of a truce extended by the country's government after the European Union gave Russia three days to quell the insurgency or face deeper sanctions.
Twelve soldiers also were wounded in the attacks by pro- Russian separatists in Ukraine's eastern region, government officials said.
The violence occurred as EU leaders in Brussels demanded on Friday that the separatists, whom Ukraine and its allies say are backed by Russian President Vladimir Putin, abide by a cease-fire that Ukrainian President Petro Poroshenko had extended through Monday, release hostages and start talks to implement a peace plan.
Rebel leaders agreed to the extension, according to news service Interfax. Still, the defense ministry in Kiev said Saturday's casualties occurred in two separate incidents.
"Despite peace initiatives by Ukraine's leadership and a unilateral cease-fire, the situation in the Eastern regions continues to escalate," the ministry said in a statement. "Insurgents are ignoring the peace plan to ease the situation in Ukraine's east and keep attacking troops."
Rebels in eastern Ukraine did release a total of eight monitors from the Organization for Security and Co-operation in Europe who had been held hostage since late May, according to accounts from the OSCE and Alexander Maltsev, a separatist spokesman for the self-proclaimed Donetsk People's Republic.
Other people not associated with the OSCE are still being held in the region.
The EU leaders said that failure to meet their demands will result in "further significant restrictive measures" against Russia, according to a statement issued on Friday.
"If no visible progress is made on these points, then we are prepared to take further decisions, including drastic measures," German Chancellor Angela Merkel said after the meeting. "We expect progress to come really in the hours ahead."
The U.S. blames Putin for supporting rebels and stoking violence the United Nations says has killed more than 400 people in the country of more than 40 million. The U.S. is preparing sanctions against Russia on technology aimed at exploiting and producing oil and gas products, a major part of that country's economy, according to three people briefed on the plans.
The U.S. and European allies imposed sanctions about two months ago on a small number of people and companies close to Putin.
The U.S. is pushing Ukraine into conflict with Russia, Russian Foreign Minister Sergei Lavrov said on Saturday, adding that the government in Kiev must consult with those in the country who are seeking more autonomy.
"There are our partners from overseas, our American colleagues who, based on plentiful evidence, still prefer to push the Ukrainian authorities along the confrontational road," Lavrov said on state-run television.
He also said that while separatists in eastern Ukraine's self-proclaimed republics of Donetsk and Luhansk listen to Moscow, they don't respond to all requests from the Kremlin.
Poroshenko signed a free-trade pact on Friday with the 28- member EU to bolster solidarity with the richer nations to Ukraine's west. He said the agreement showed Ukraine's "sovereign choice in favor of future membership of the EU."
"We're just looking to modernize our country," Poroshenko said in an interview in the French daily Le Figaro published Saturday. "We introduce freedom, democracy and rule of law, European values, and we're being attacked because of it."
A previous rejection of the trade accord by the man Poroshenko replaced, Viktor Yanukovych, triggered deadly protests in Kiev last November that this year ousted the pro- Russian administration. Russia responded by annexing Crimea from Ukraine and has voiced support for Russian speakers in Ukraine's southeast, who it says are under attack by their own government.
About 67 percent of Ukrainians would vote to join the EU in a referendum, according to a June 6-11 Razumkov Center poll of 2,012 voters, versus 20 percent who wouldn't.
While the deal doesn't offer EU membership, it gives Ukrainian companies better access to the world's biggest trading bloc and will boost exports by 1 billion euros ($1.4 billion) a year, according to an EU estimate. In exchange, Ukraine pledged to use EU funds to meet product, safety and consumer standards, bolster human rights and fight graft.
Putin, who is trying to establish a Eurasian trading bloc made up of former Soviet states to rival the EU, has said the agreement will damage Russia's economy. His government has said those who sign agreements with the EU may face repercussions.
In Saturday's violence, insurgents killed three soldiers and wounded four at a checkpoint in the Donetsk rebel stronghold of Slovyansk, military spokesman Oleksiy Dmytrashkovskyi said.
Two other soldiers were killed and eight wounded in an attack by insurgents in the Luhansk region, he said.
There were no details on rebel casualties.
More than 20 Ukrainian soldiers have died in rebel attacks since the cease-fire began, Interior Minister Arsen Avakov said on Friday.
The EU has imposed asset freezes and travel bans on 61 people connected with unrest in Ukraine and Russia's seizure of Crimea in March. It has stopped short of broader curbs on investment and trade that might damage the European economy as it shakes off the effects of the debt crisis.
Russia's economy can withstand sectoral sanctions, though a worst-case scenario would result in an economic contraction, higher inflation, and declining incomes and government reserves, Russian Economy Minister Alexei Ulyukayev said on state-run TV Saturday.
The UN estimates that about 54,000 people have fled to other places inside Ukraine, while 110,000 displaced Ukrainians have arrived in Russia this year.
Russia's failure to comply with the EU deadline could lead to additional asset freezes and travel bans after Monday, June 30. A move toward more sanctions could come as early as mid-July, when the leaders are scheduled to meet again.
EU sanctions require a consensus of the bloc's 28 governments, making it possible for countries such as Austria, Slovakia or Italy to stand in the way. Austria deepened its economic ties with Russia last week by signing an accord with OAO Gazprom for direct pipeline access to Russian gas.
"The important thing is that for the very first time in history we — the EU and Ukraine — agreed on a common stance vis-a-vis Russia," Polish Prime Minister Donald Tusk told reporters in Brussels on June 27.
Neuger reported from Brussels. With assistance from Daria Marchak, Daryna Krasnolutska and Kateryna Choursina in Kiev, Patrick Donahue and Ewa Krukowska in Brussels, Scott Rose and Stepan Kravchenko in Moscow, Roger Runningen and Phil Mattingly in Washington and Katherine A O'Neill in New York