BANGKOK (AFP) - Thailand's ruling party on Friday warned that anti-government protests in the capital could descend into violence, accusing a key opposition leader of stashing "weapons" at the rally site.

Demonstrators angry at an amnesty proposal that may have allowed the return of self-exiled former premier Thaksin Shinawatra, have remained on Bangkok's streets despite the parliamentary defeat of the controversial Bill.

"There are war weapons being kept in the middle of the protest. I want to tell people who might want to go to the rally today to stay home," Mr Suporn Atthawong, deputy secretary to Prime Minister Yingluck Shinawatra, told reporters.

Mr Suporn, a key member of the pro-Thaksin "Red Shirts", did not elaborate on what type of arms he believed were at the rally site in the historical centre of the capital. His claims were swiftly rejected by protest organisers.

The rallies, which drew some 2,000 people by midday Friday, are the latest in a long and sometimes bloody series of political rallies in turbulent Thailand in recent years.

"I can confirm that their goal is now to overthrow government," said Mr Suporn, who is widely known by the nickname "Rambo Isaan", referring to a region in northeast Thailand considered as Thaksin's heartland.

He accused rally leader and former deputy premier Mr Suthep Thaugsuban of plotting unrest.

Protest spokesman Mr Akanat Promphan said there was "not a single weapon" at the site.

"No one believes this story and you can see that by the high attendance," he said.

Experts say the opposition Democrat Party, which Suthep resigned from to head the protests, has benefited from anger over the amnesty.

Up to 50,000 people gathered in Bangkok on Monday evening to voice their discontent, blowing whistles, chanting and waving Thai flags.