By Petar Komnenic
PODGORICA (Reuters) - Several thousand protesters demanding the resignation of Prime Minister Milo Djukanovic and the formation of an interim government marched in the centre of the capital Podgorica on Sunday evening.
Police units cordoned off state institutions, including a parliament building and government headquarters where Djukanovic has his office. A small group of masked men clashed with police as they tried to approach the building and police fired teargas, a Reuters witness reported.
Andrija Mandic, a leader of the ex-Yugoslav republic's main opposition bloc the Democratic Front, which organised the demonstration urged protesters to refrain from violence. He said that the protests will continue unless their demands are met by Saturday.
"If until Saturday an interim government is not formed and Djukanovic is not gone, people from all over Montenegro will come to Podgorica," Mandic said.
Earlier on Sunday, the country's ruling coalition and opposition parties agreed to call an extraordinary session of the parliament's security committee to investigate whether the police had used excessive force at an opposition rally on Saturday.
The National Security Council concluded that during the three-week long protests "there were activities that threatened the constitutional order, stability and security of the citizens and their property."
It said the police action "had been cased by unlawful behaviour and active resistance of the participants."
Djukanovic's Democratic Party of Socialists (DPS) accused the Democratic Front of trying to stop it from joining NATO, it said in a statement on Sunday.
The Democratic Front's supporters and MPs, set up tents in front of the parliament three weeks ago, but police removed the tents early on Saturday morning to unblock the city's main street, prompting the Democratic Front to call for the evening protests.
Demonstrators hurled bottles at the police who responded by firing teargas and beating some people at the front of the crowd, including prominent opposition leader Nebojsa Medojevic, a Reuters witness said.
The police said 15 demonstrators were detained and four police officers were injured.
Montenegro is a candidate for European Union membership and is also expecting an invitation to join NATO later this year.
But Western governments and rights groups remain concerned over the level of organised crime and graft, which especially flourished during the breakup of Yugoslavia in the 1990s.
Montenegro will hold a parliamentary election next year.
Critics say the Adriatic country of 680,000 is run as a fief by a political elite largely unchanged over the past 20 years, a description the government rejects.
(Reporting by Ivana Sekularac, editing by Louise Heavens)