Government's failure to grant key concessions met with anger in the capital, with protests spreading to other parts of country

Opposition leaders begged protesters in Kiev to keep observing a truce with riot police late on Thursday night, after long talks with President Viktor Yanukovych ended without a major breakthrough.

The government's failure to grant key concessions was met with anger by thousands of protesters manning the barricades in the capital, while the anti-government protests that have rocked Ukraine spread to other parts of the country during the day.

On Wednesday, after three people had been killed in clashes with riot police, opposition politician Vitali Klitschko had asked protesters in central Kiev to observe an eight-hour truce while talks went on. Klitschko had promised to "go on the attack" if Yanukovych did not launch snap elections within 24 hours, while Arseniy Yatsenyuk of the Fatherland party said he was ready to take a "bullet in the head".

The protesters duly extinguished the flaming barricade of tyres that had been set up on the frontline, and the two sides stood facing each other down, the carcasses of burned out police buses between them. But when the trio of opposition leaders emerged after gruelling talks with the president that lasted more than four hours, they had changed their tune, asking for more time and a continuation of the ceasefire.

"The only thing we were able to achieve was not much," a grim Klitschko told the crowd. He was booed by some of those at the barricade as he asked for a truce.

Opposition leader and former WBC heavyweight boxing champion Vitali Klitschko addresses protesters near the burning barricades in central Kiev. Photograph: Sergei Chuzavkov/AP

The fires were lit again and the capital was set for an uneasy night. On Independence Square nationalist leader Oleh Tyahnybok, who was part of the negotiations, put the idea of continuing discussions with the president to a midnight vote among the crowd, and it was overwhelmingly rejected. There are now difficult decisions for the opposition leaders, who have been unable to achieve their key demand of snap elections from Yanukovych but are uneasy about being held responsible for any further violence.

Earlier in the day Yanukovych suggested holding an emergency parliament session next Tuesday in the hope of ending the standoff, though this alone was unlikely to placate protesters.

There were dramatic developments in the west of the country too on Thursday as hundreds of people forced their way into the office of the regional governor in the city of Lviv, and forced him to sign a resignation letter.

The governor, Oleh Salo, a Yanukovych appointee in a city where support for the president is in low single digits, later said he signed the letter under duress and was rescinding his resignation.

A pro-European integration protester carries tyres at the site of clashes with riot police in Kiev. Photograph: Valentyn Ogirenko/REUTERS

In the city of Rivne the regional administration building was stormed by thousands rushed in, demanding those detained in protests be freed, while reports of similar events came in from other towns.

Tensions were inflamed by mounting evidence of police brutality against protesters, as photographs and videos, that appearing to show ill treatment of detainees, spread across Ukrainian social media.

In one video a detainee, named by protest organisers as Mikhailo Gavrilyak, was stripped naked and made to walk around in the snow while several riot police officers posed for photographs and one slapped him on the back of the head. The interior ministry apologised for "the impermissible actions of people wearing police uniforms" in a statement about the incident. There were also reports of detainees being arrested then taken not to police stations but out to forests and manhandled.

Andriy Tarasenko, who claims to represent the far-right group Pravy Sektor, which has taken responsibility for much of the violent response to riot police, told the Guardian that the group's members were likely to continue guerilla warfare if Yanukovych did not resign.

Ukraine's prime minister, Mykola Azarov, in Davos at the World Economic Forum, said "a genuine attempt at a coup d'état" was being carried out in Kiev. He had been due to participate in a panel at the forum on Friday but was barred in protest at the clashes in Kiev.

"All those who support this coup should say clearly, 'yes, we are for the overthrow of the legitimate authorities in Ukraine', and not hide behind peaceful protesters," Azarov said. However, he later said that controversial new anti-protest laws, which came into force on Tuesday, could be improved if there was proper dialogue with the opposition.

The interior ministry claimed the bullets that killed two men in clashes on Wednesday were not of a type used by any police or troops. The authorities have suggested the deaths could have been due to provocateurs.

A diplomatic initiative to stop the bloodshed gathered pace on Thursday, as Yanukovych fielded calls from a number of European politicians and US vice president Joseph Biden. Additionally, the former former Soviet leader Mikhail Gorbachev called on the US president, Barack Obama, and Russia's Vladimir Putin, to help find a negotiated settlement to Ukraine's conflict.

In a letter published on his website on Thursday Gorbachev, who has Ukrainian heritage, said: "Without the help, without the co-operation of authoritative representatives of our two countries this [situation] could lead to catastrophe … I ask you to seize the opportunity and take a decisive step to help Ukraine return to the path of peaceful development. I am really relying on you."