The BBC's Caroline Gluck: "Opposition parties have denied any involvement in the attack"

In a statement issued via a spokesperson for his party, Mr Rainsy said he could assure the public that he was not involved in a grenade attack in the grounds of Second Prime Minister Hun Sen's residence in Phnom Penh earlier on Monday.

No one was injured when the two grenades exploded in the compound of Hun Sen's home - in his statement, Mr Rainsy said he had always condemned violence.

Mr Rainsy had held five hours of talks with the UN representative in Cambodia, Lakhan Mehrotra, and five other foreign diplomats and is now staying at the UN office in the Phnom Penh hotel where their discussions took place.

As the talks took place, armed police waited outside the city centre hotel and when the diplomats left the venue, five shots rang out.

Police later said they had been trying to detain a car in breach of traffic regulations. However, the BBC's correspondent in Phnom Penh, Caroline Gluck, reported that party supporters speculated that the police may have believed that one of the diplomatic vehicles was carrying Mr Rainsy.

In the early evening, riot police arrived and fired several rounds of ammunition into the air to disperse hundreds of opposition supporters gathering outside the hotel.

Security has been stepped up around the capital, with barricades and roadblocks in place.

The BBC's correspondent says the presence of riot police and their use of live ammunition against protestors hardly bodes well for a peaceful ending to the current political stalemate.

Hun Sen calls for arrest

The Second Prime Minister, Hun Sen, said all land, sea and air routes out of the country had been closed, and made appeals to foreign missions in Cambodia not to give Sam Rainsy refuge.

He also called for a round-the-clock demonstration outside parliament to be shut down by midnight on Monday following a grenade attack at his Phnom Penh residence earlier on Monday.

Sam Rainsy: Accused of being "a terrorist"

Opposition supporters have spent two weeks protesting in a park outside parliament in Phnom Penh, claiming that Hun Sen's victory in last month's general election was down to electoral fraud.

The prime minister denied the attack was a convenient pretext to quash the continuing political protest and detain opposition leaders.

He accused the opposition of trying to topple the government, encouraging the breakdown of social order and inciting violence.

The BBC's Caroline Gluck reports from Phnom Penh

Both opposition parties have vigorously rejected Hun Sen's accusations and have pledged to continue with their protest outside parliament.

Three grenades

Two bombs went off in Hun Sen's home

Police say that two grenades exploded inside the compound of his house in the capital, Phnom Penh, on Monday, causing damage but no injuries. A third lay unexploded on the pavement outside.

At the time of the attack Hun Sen was in the northern town of Siem Reap holding talks with opposition leaders in a bid to end the dispute over the election result.

But on hearing of the attack, Hun Sen immediately broke off the negotiations.

Before returning to the capital to be briefed by military and security officials, he told reporters the attack was a terrorist act, comparing it to an attempted coup.

Hun Sen said that while Sam Rainsy had made speeches urging the armed forces to kill him, it was up to the authorities to decide if they also had enough evidence to prosecute Prince Norodom Ranariddh, the head of the royalist party, Funcinpec.