Beirut : Hundreds of thousands of Hezbollah-led protesters rallied on Friday at the doorstep of Prime Minister Fouad Siniora to force the resignation of his US-backed government.

"We want a clean government," one banner read. "Siniora out, we want a free, free government," the crowd chanted.

Hezbollah, Lebanon's most powerful Shiite Muslim group, and its pro-Syrian allies had called on Lebanese from across the country to take part in the protest in the capital Beirut, to be followed by an indefinite sit-in near the government offices.

"I call on the prime minister and his ministers to quit," Christian opposition leader Michel Aoun said to the cheers of protesters in downtown Beirut. Speaking on behalf of the opposition, Aoun demanded a national unity government.

A senior opposition source said opposition supporters were imposing an open-ended blockade to the government offices where Siniora and and most of his ministers were holed up.

"Tents are being put up for protesters to encircle the government's headquarters to stop movements to and from it until Siniora falls," the source said.

Large numbers of security forces, backed by armoured troop carriers, were deployed.

Druze leader Walid Junblatt, the most prominent anti-Syrian leader, urged supporters to remain calm and avoid street confrontations. He said Hezbollah wanted to instate Syrian and Iranian tutelage over the country.

"Very calmly, we will remain steadfast," he told a news conference yesterday. "We will confront [the opposition] calmly. We will remain in our houses and fly the Lebanese flags ... We will wait for a month, for two months ... and watch them."

Late on Thursday Siniora went on television to vow that his cabinet would not be cowed. It would fight the return of any foreign tutelage on the country, he said, in an apparent reference to Syria.