Thousands of Lebonese troops and police mobilized Thursday to block an unauthorized demonstration outside the US Embassy aimed at protesting "American-British collusion" with Israel in a dramatic prison raid in Jericho earlier this week. Several thousand troops in armored vehicles and police in trucks 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 began to back up for miles on the coastal highway, according to witnesses. 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. Authorities appeared to be preventing the demonstrators from reaching the embassy, which is located in the hilly 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 organizers, 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.