Thousands of protesters from rural northern Thailand have begun arriving in Bangkok for a rally aimed at toppling the government of Thai Prime Minister Abhisit Vejjajhiva.

Trucks and other vehicles filled highways into the capital city Saturday as security forces searched them, ahead of a protest scheduled for Sunday to restore ousted Prime Minister Thaksin Shinawatra to power.

Protest organizers say between 600,000 and 700,000 supporters of the United Front for Democracy Against Dictatorship (UDD) will march in Bangkok.

About 50,000 police, military and other security forces were patrolling Bangkok. The government has enacted an internal security law that allows the military to impose curfews and restrict freedom of movement.