Bangkok, Thailand ? Tens of thousands of protesters demanding the prime minister’s resignation marched to his office Sunday night after a boisterous rally accusing Thaksin Shinawatra of corruption and abuse of power.

Leaders vowed the crowds would camp out in the streets until Thaksin quit.

Marchers were stopped by a police line near Democracy Monument – the site of bloody pro-democracy demonstrations in 1973, 1976 and 1992. But protest leaders negotiated with authorities and won permission to continue to Government House, the prime minister’s office.

Thaksin was believed to be in northeastern Thailand.

The anti-Thaksin campaign swelled last month after the prime minister’s family sold its controlling stake in telecommunications giant Shin Corp. to a Singapore state-owned investment company, netting $1.9 billion.

Critics allege the sale involved insider trading and tax dodges and complain that a key national asset is now in the hands of a foreign government.