Thai opposition groups are gathering for a mass protest against Prime Minister Thaksin Shinawatra, pledging to camp out in the capital until the embattled leader resigns.

Spearheaded by the People's Alliance for Democracy, demonstrators have planned a late afternoon rally at Bangkok's Sanam Luang (Royal Field).

The area has been the site of three bloody pro-democracy demonstrations in past years (1973, 1976, 1992).

After a month of street protests demanding his resignation, Mr. Thaksin abruptly dissolved parliament on February 24 and called a general election for April 2, three years ahead of schedule, in a bid to defuse the crisis.

The country's three main opposition parties (Chart Thai, Democrat, Muan Chon) say they will boycott the polls. They accuse Mr. Thaksin of corruption and criticize his family's nearly $2 billion, tax-free stock sale of its telecom business.

Some information for this report provided by AP and AFP.