A top Ukrainian opposition leader on Thursday urged protesters to maintain a shaky truce with police after at least two demonstrators were killed in clashes this week, but some in the crowd appeared defiant, jeering and chanting "revolution" and "shame."

Emerging from hours-long talks with President Viktor Yanukovych, opposition leader Oleh Tyahnybok asked demonstrators in Kiev for several more days of a truce, saying the president has agreed to ensure the release of dozens of detained protesters and stop further detentions.

But other opposition leaders offered mixed reports on the outcome of the meeting, with Vitali Klitschko saying negotiations had achieved little.

He and Tyanhnybok were booed at the barricades by angry demonstrators and the atmosphere appeared tense.

"We are not going to sit and wait for nobody-knows-what," said Andriy Pilkevich, a ski mask-wearing protester who was building barricades near police lines from giant bags of ice. "Those who want to win must fight."

Interior Minister Vitali Zakharchenko issued a statement guaranteeing that police would not take action against the large protest camp on Independence Square, known as the Maidan. He also called on the police to exercise calm and not react to provocations.

The developments came as hundreds of enraged protesters in several regions in western Ukraine, where Yanukovych has little support, seized government offices and forced one governor loyal to Yanukovych to resign.

At least two people were killed by gunfire Wednesday at the site of clashes in Kiev. Demonstrators had pelted riot police with barrages of stones and set police buses on fire, while the officers responded with rubber bullets, tear gas and stun grenades.

Opposition leaders had set a Thursday evening deadline for the government to make concessions or face renewed clashes. Protesters had quenched barricades that had been set on fire, but lit them again during the evening.

Although one opposition leader, Arseniy Yatsenyuk, said after the talks that "there is a really good chance" of stopping the bloodshed, Klitschko was more downbeat.

"The only thing we were able to achieve was not much," a grim Klitschko told the crowd.

He urged protesters to refrain from violence and continue peaceful protests to avoid further bloodshed.

"I am afraid, yes, I am afraid of human losses," Klitschko said. "We will be widening the territory of the Maidan further until these guys start reckoning with us."

The president called a special session of parliament next week to discuss the tensions, telling the parliament speaker: "The situation demands an urgent settlement." But there was no indication that the move represented a compromise, since the president's backers hold a majority of seats.

The protests began two months ago after Yanukovych turned away from closer ties with the European Union in favor of getting a bailout loan from Russia. They turned violent this week after he pushed through harsh anti-protest laws, rejecting protesters' demands that he resign and call new elections.

On Thursday, the violence spread to western Ukraine, where support for Yanukovych is thin and most residents want closer ties to the 28-nation EU.

In Lviv, near the Polish border some 450 kilometers (280 miles) west of Kiev, hundreds of activists burst into the office of the regional governor, Oleh Salo, a Yanukovych appointee, shouting "Revolution!"

After surrounding him and forcing him to sign a resignation letter, an activist ripped it out of Salo's hands and lifted it up to the cheers and applause of the crowd. Salo later retracted his signature, saying he had been coerced.

Meanwhile, hundreds of protesters smashed windows, broke doors and stormed into the governor's office in the city of Rivne, shouting "Down with the gang!" — a common reference to Yanukovych's government. Once inside, they sang the national anthem.

Angry crowds also besieged government offices in other western regions.

Meanwhile, anger spread after a video was released online appearing to show police abusing and humiliating a naked protester in what looked like a location close to the site of the Kiev clashes.

In the video, a young man wearing nothing but socks, his body covered with multiple bruises, was forced to stand in the snow in freezing temperatures as a policeman punched him in the head and others forced him to pose for photos.

The Interior Ministry issued a statement apologizing "for the impermissible actions of people wearing police uniforms" and said it had launched an investigation into the incident.

The protests have been centered on Kiev's main square, where demonstrators have defended a large tent camp for nearly two months. On Wednesday, riot police moved to dismantle barricades erected next to a government district and two people were fatally shot in the clashes.

The opposition has blamed the deaths on authorities, but Prime Minister Mykola Azarov said Thursday that the two men's wounds were caused by hunting rifles, which the police do not possess. The Interior Ministry said the men could have been killed in order to escalate the crisis.

The opposition maintains that as many as five people died in Wednesday's clashes, though they say they have no evidence because the bodies were removed by authorities.

The Interior Ministry said Thursday that 73 people had been taken into custody, including 52 being investigated for "mass riots" — a new criminal charge that carries a prison sentence of up to eight years.

Reaction from the West and neighboring Russia has been mixed.

The United States has revoked the visas of Ukrainian officials linked to violence and threatened more sanctions. On Thursday, Vice President Joe Biden called Yanukovych and urged him to immediately de-escalate the standoff in Kiev and end the bloodshed. The White House said Biden also called on the Ukrainian leader to address the protesters' legitimate concerns and protect democratic freedoms.

EU Commission President Jose Manuel Barroso said Thursday that if the situation in Ukraine does not stabilize, the EU "would assess possible consequences in its relationship." Barroso also said he had received assurances from Yanukovych that the Ukrainian leader did not foresee the need to impose a state of emergency.

German Chancellor Angela Merkel said this wasn't the time to consider sanctions against the Ukrainian government, but added that it must comply "with its obligations to secure fundamental democratic rights."

Russia, in turn, accused the West of meddling in Ukraine's affairs.

"We feel regret and indignation about the obvious foreign interference in the developments in Kiev," Russian President Vladimir Putin's spokesman, Dmitry Peskov, told the daily Komsomolskaya Pravda.