A Thai opposition group vowed on Sunday to hold more anti-government street rallies in Bangkok in a bid to force the government of Prime Minister Samak Sundaravej to step down.

"We will stay here until the government resigns," Somsak Kosaisuk, one of the People's Alliance for Democracy (PAD) leaders, told Reuters by telephone from the rally at the Makawan Rangsan bridge near the Grand Palace in the heart of Bangkok.

His remarks came a day after Samak appeared to back off from a threat to crack down on the protests that have ignited fears of a military coup.

The PAD, a coalition of civic groups, and the opposition Democrat Party accuse Samak's government of being a puppet of former Prime Minister Thaksin Shinawatra.

The rallies which began a week ago are similar to the PAD's street campaign against Thaksin before he was ousted in a 2006 coup. The protests two years ago started small but grew to 100,000-strong crowds before the military intervened.

Saturday's rally swelled to 6,500 protesters watched by several hundred police with shields and batons.

The crowd had thinned to around 400-500 by Sunday morning, but PAD leader Somsak said he expected numbers to grow later and they would be alert to any attempt to break up the rally.

In an address to the nation on Saturday morning, Samak had threatened to crack down on the protests and several hundred riot police were deployed along with hundreds more in reserve.

But as night fell, Interior Minister Chalerm Yubamrung said police would not move against the mainly middle-class crowd, who appeared in a festive mood.

On Sunday, Samak said on his weekly television program that he had never intended to disperse the crowd by force and he accused the media of distorting his remarks made a day earlier.

"I made no threatening words. You (the media) all interpreted what I said wrongly," Samak said on his regular one-hour program, where he takes on a range of topics and often attacks his critics.

But Samak maintained that the PAD had broken the law and must move away from the Makawan Rangsan bridge where the gathering has caused traffic congestion and shut a 1 km stretch of a six-lane road for nearly a week.

Police said they have issued no ultimatum to the protesters.

"We will talk peacefully to them about when they should move. We will not cause any violence," deputy police spokesman Surapol Thuanthong said.

Violence stemming from a clampdown on the rally could add to concerns about the army being drawn back into the political fray, particularly after scuffles broke out between pro- and anti-Thaksin protesters at a rally last Sunday.

Thailand's top military commander, who last week denied rumours the army was plotting a coup, said on Saturday soldiers were unlikely to be used to quell the protests.