With the security dragnet on Thursday, the protest was muzzled, and only a handful of protesters managed to get to within a couple of kilometers of the compound.

Several thousand troops in armoured vehicles and police in trucks were deployed to major roads north and south of Beirut, setting up checkpoints to search cars for weapons and check identification of passengers, security officials said. Traffic backed up for kilometres on the coastal highway, witnesses said.

Similar measures were taken in southern Lebanon, with witnesses reporting troops blocking roads leading out of Palestinian refugee camps in the port city of Sidon to prevent protesters from heading to Beirut.

The authorities appeared to be preventing the demonstrators from reaching the embassy, which is in the suburb of Aukar, north of the city. Only a few protesters managed to get to the coastal road, down the hill from the compound.

Two of the organisers, Mohammed Safa and Bassam Kintar, were detained by police, the two said by cellular phone to the al-Manar TV station.

The security measures signified a new and tougher stance by authorities against protests by groups not allied with the government.

"They are not allowed to normally demonstrate," he said. "But at the same time we do not seek to ban legal protests"

Ahmed Fatfat, Lebanon's acting interior minister

Acting Interior Minister Ahmed Fatfat said organisers did not receive permission.

"They are not allowed to normally demonstrate," he said. "But at the same time we do not seek to ban legal protests."

Fatfat said security forces would take action if protesters resort to violence. "The security forces, with the help of the army, will provide security to the people if the law is broken," he said on LBC television.

The demonstration was called by the Arab Organisation for Defending Detainees and other groups to protest against the raid in the West Bank town of Jericho in which Israel spirited away six members of resistance groups, including Ahmed Saadat, the alleged mastermind of the 2001 assassination of an Israeli cabinet minister.

The protest was "in solidarity with the struggler Ahmed Saadat and his comrades", the organisation said in a statement.

Syria sit-in

In Damascus, about 150 Palestinians staged a sit-in outside the Red Cross headquarters to protest against the Israeli raid and to criticise the Palestinian Authority for having advance information about the pullback of US and British observers before the raid.

"From Jericho to Abu Ghraib to Guantanamo, the Mask of the Neo-Nazi's Have Fallen," read a banner raised by the protesters. "The Raid is a Stain on the Palestinian Authority's Forehead," read another.