Police in Kyrgyzstan have used tear gas in the capital, Bishkek, to disperse hundreds of protesters who had occupied part of the main government building.
Protesters broke through the railings surrounding the building
At least 20 people are said to have been hurt in the unrest, which saw protesters driven into side streets.
The demonstrators support a candidate barred from July's presidential poll, but the acting leader has blamed the unrest on followers of his predecessor.
Kyrgyzstan has seen continuing tension since the former leader fled in March.
Kurmanbek Bakiev became acting president after a wave of protests sparked by disputed parliamentary elections.
He warned the authorities were ready to use force if required, following Friday's unrest.
"I will defend this government with a gun in my hands if necessary," he said.
The BBC's Ian MacWilliam, in the region, says the interim government has struggled to assert its authority since coming to power.
Various interest groups have decided demonstrations are the best way to force the government to acknowledge their complaints, he adds.
Friday's incident is the biggest public protest since former President Askar Akayev was driven into exile.
The unrest came after some 1,000 people rallied in Bishkek in support of businessman Urmatbek Baryktabasov, whom officials say is a citizen of neighbouring Kazakhstan.
13 June: Security guards open fire on protesters in Osh, injuring at least seven
10 June: Politician Jyrgalbek Surabaldiyev shot dead in Bishkek
1 June: Hundreds eject protesters from Supreme Court which they had held for more than a month
Protesters also called for Mr Bakiev to step down.
Officials fled the site when the crowd broke into the government complex in the city centre.
Police and troops armed with truncheons and shields ousted them first from the building and finally from the adjoining square.
Speaking after the incident, Mr Bakiev told reporters "events were organised by people close to Akayev".
"I will not run away," he added.
The acting defence minister told the parliamentary session that armed forces would be deployed on Friday night to maintain order.
Shops in the area have closed for fear of the looting that followed the March uprising.