Thai prosecutors will appeal against a court decision rejecting a US request to extradite a Russian-born alleged arms dealer detained in the capital Bangkok.

Victor Bout, who has been called the Merchant of Death, has been fighting extradition since his March 2008 arrest accused of agreeing to supply missiles to Colombian rebels.

On Tuesday, a Bangkok court said that it did not have the authority to order the extradition of the 42-year-old because the Revolutionary Armed Forces of Colombia (Farc) was not listed as a terrorist group in Thailand.

But according to Sirisak Tiyapan, executive director of international affairs at the
Thai foreign office, the country's state prosecutor formally told the court on
Thursday that he would lodge an appeal against the ruling.

"The prosecutor has told the court that he intends to appeal against the decision. We are in the process of seeking the official  ruling," Sirisak told AFP news agency.

Sirisak also said that the prosecutor has 30 days in which to actually lodge the appeal, during which time Bout would remain in prison.

The court had given the government until Friday to say whether it would
appeal.

'Disappointed and mystified'

News of the appeal came after the US said it was "disappointed and mystified" by the court's decision to reject Bout's extradition and hoped that the Thai government would appeal against the decision.

Bout a former Soviet air force officer, was arrested in a sting at a five-star hotel in the Thai capital after allegedly agreeing to supply surface-to-air missiles to US agents posing as rebels from Farc.

He had faced life in prison if sent to the US and convicted there on terrorism charges, including conspiracy to kill US officers or employees and conspiracy to acquire and use an anti-aircraft missile.

He denies the charges and insists that he ran a legitimate air cargo business.