DONETSK, Ukraine -- The Interior Ministry headquarters in eastern Ukraine's largest city fell to pro-Russia separatists Tuesday after a five-hour gunbattle that erupted hours after the Ukrainian president ended a cease-fire.
The shaky cease-fire had given European leaders 10 days to search for a peaceful settlement, and its end raised the prospect that fighting could flare with new intensity in a conflict that has already killed more than 400 people since April.
In Tuesday's clashes, rebels fought for more ground, and badly trained and disorganized government troops seemed incapable of crushing the mutiny.
President Petro Poroshenko had called a unilateral cease-fire to try to persuade the rebels to lay down their weapons and hold peace talks. Some of the rebels signed onto the break in fighting as tentative negotiations began, but each side accused the other of repeated violations. When he ended the cease-fire, the president said the rebels were not serious about peace.
In Moscow, Russian President Vladimir Putin argued that substantive talks with representatives in eastern Ukraine had failed to start in earnest and that the cease-fire announced by Poroshenko amounted to an ultimatum to the rebels to disarm.
The Russian leader also denounced the Western threat of sanctions as blackmail, adding that Moscow wouldn't accept "ultimatums and mentor's tone."
Europe must not allow "any unconstitutional coups and interference into the domestic affairs of sovereign states" and should steer clear of "inciting radical and neo-Nazi forces" to avoid destabilization, Putin said.
Russia has cast February's ouster of Ukraine's former pro-Moscow president following massive protests as a coup conducted by radical nationalists and neo-Nazis.
In Donetsk, the capital of Ukraine's eastern industrial heartland, many streets were deserted, and gunfire filled the air Tuesday as rebels besieged the headquarters of the regional Interior Ministry. The rebels eventually captured the compound, leaving the body of a plainclothes police officer outside.
In Kiev, the interior minister said Ukrainian forces had repelled the rebel attack in Donetsk, but an AP journalist on the ground saw that clearly was not the case.
Panicked residents fled the fighting.
"I was driving and some people appeared with automatic weapons," said a man named Vitaly, who said he was too fearful to give his last name. "They put me and my girlfriend on the ground and then they said: 'Run away from here!'
"I don't know who is fighting whom. We are standing here. We are afraid and shaking."
It was not clear what prompted the rebel attack on the Interior Ministry building, which houses regional police, who have peacefully coexisted with the rebels even though they still officially answer to the central government in Kiev.
The Interfax news agency quoted Sergei Kavtaradze, a spokesman for the insurgents in Donetsk, as saying the attack was launched by militants from the neighboring Luhansk region. There was no way to immediately confirm his claim.
Poroshenko announced the end of the cease-fire late Monday. By early Tuesday, the military had made artillery and airstrikes against separatist positions, Defense Ministry spokesman Oleksiy Dmytrashkovsky told the Interfax news agency.
He said one service member was killed and 17 wounded in the previous 24 hours, and that a military jet was damaged.
There was no comment on any casualties from the rebel side.
Near the village of Karlovka, 30 kilometers (20 miles) northwest of Donetsk, residents told The Associated Press that government forces and rebels began firing heavy weapons at each other across a bridge early Tuesday, just hours after the cease-fire expired.
"There was shooting near the water. Even the water was splattering," said Inna Vladimirovna, who gave only her name and patronymic, fearful of being identified. "We know when they are just shooting to scare and when they are shooting to kill."
Ukrainian troops appeared to score some success Tuesday, with Poroshenko congratulating them on dislodging rebels from one of the three checkpoints on the border with Russia that the separatists had seized.
European leaders have been pressing Putin to persuade the rebels to lay down their weapons. The West has accused Russia of fomenting the rebellion with troops and weapons.
Russia has rejected those claims, saying that Russians who crossed into the east to fight with the rebels were private citizens. It says its influence with the rebels is limited and urges the Ukrainian government to negotiate directly with them.
Putin warned Tuesday that by ending the cease-fire, Poroshenko had made himself politically responsible for the fighting that began months before he was inaugurated in early June.
Over the last two days, Poroshenko held four-way phone talks for hours with Putin, German Chancellor Angela Merkel and French President Francois Hollande but said the rebels' failure to meet his conditions made it impossible to extend the cease-fire.
On Wednesday, foreign ministers of France, Germany, Russia and Ukraine are set to meet in Berlin to continue searching for a settlement.
In Brussels, the European Union's 28 governments decided Tuesday they were not ready to hit Russia with a new round of sanctions over Ukraine and put off a decision until Monday, according to an EU official.
The sanctions would target those responsible for fomenting unrest in eastern Ukraine, according to a diplomat from a major EU country, and could include travel bans and asset freezes for both individuals and companies. The EU has so far sanctioned only individuals.
Both the EU official and the diplomat spoke on condition of anonymity because they were not allowed to discuss the closed-door talks publicly.