The Armenian president has declared a state of emergency following clashes between riot police and protesters angry at the outcome of a presidential election.

The state of emergency will be in effect until 20 March under a decree signed by President Robert Kocharian.

Mr Kocharyan vowed to use the army against protesters occupying the centre of the capital, saying they were using weapons.

Protesters in the capital Yerevan set dozens of cars on fire and looted shops following clashes with police over the disputed election.

The protesters had massed in Yerevan for an 11th consecutive day protesting alleged rigging of a 19 February presidential election.

The opposition's show of defiance came after riot police stormed Yerevan's Freedom Square to clear a hard core of some 1,500 protesters who had been camping there around the clock since the  election.

Police could be seen beating several protestors and the health ministry reported that 31 people, including six police officers, had been injured in the operation.

Opposition chief Levon Ter-Petrosian, the defeated presidential candidate and former president of the mountainous country, said he had been placed under house arrest following the crackdown.

Protesters claim the election was rigged to ensure victory for Prime Minister Serzh Sarkisian, a close ally of the outgoing president.