Police will ask the court to approve an arrest warrant for red-shirt core member Petchawat Wattanapongsirikul after he made a threatening comment to Prime Minister Abhisit Vejjajiva.

United Front for Democracy against Dictatorship (UDD) leader Petchawat earlier said on a community radio station that Mr Abhisit could be killed in a car bomb attack during his visit to Chiang Mai to attend the provincial chamber of commerce meeting on Nov 29. The anti-government group later defended Mr Petchawat, saying he was only joking and there was no assassination plan against the premier.

The police will submit the evidence to the provincial court to seek an arrest warrant for Mr Petchawat on Monday, Chiang Mai deputy governor Phairoj Sangphuwong said on Sunday.

"This is a state criminal case that does not require a prosecutor, as officials can file charges against the guilty party," Mr Phairoj said. "However it would be difficult to shut down the community radio station since the province has no authority and there are no clear regulations on this."

Mr Petchawat has more than 10 pending cases against him, the deputy governor said.

During Mr Abhisit's visit to Chiang Mai next weekend, officials from all districts of Chiang Mai and the Interior Ministry had asked people not to join the red-shirt rally following the news on potential violence.