Left-wing rebels in Colombia say they have kidnapped two foreign journalists because they entered a region held by the group without permission.

The ELN specialises in kidnappings

The National Liberation Army, or ELN, said the pair were "retained" at a rebel roadblock in the Arauca state in the town of Saravena, about 205 miles (330 km) north east of the capital, Bogota.

They were led at gunpoint from their taxi with hoods on their heads to an unidentified rebel camp, their driver told the Associated Press news agency.

Named as American Scott Dalton and British national Ruth Morris, the pair were on a freelance assignment when they were detained.

The news comes as one American-Canadian and two American citizens kidnapped by right-wing paramilitary guerrillas last Saturday were freed by their captors.

'War footing'

A broadcast by an ELN radio station said that Ms Morris and Mr Dalton, who were on an assignment for the Los Angeles Times newspaper, would be freed "when the time is right" and when "merited by political and military conditions", Reuters news agency reported.

Both the AUC and ELN are considered terrorist organisations by the US

The group, which said it would guarantee the safety of the pair, did not give specific reasons for the kidnapping, other than a complaint that the local Colombian army unit had been assaulting locals.

Arauca was recently declared a war zone by the Colombian Government, giving the military power to control people's movements and ELN said in the broadcast that as a result they were on "a war footing".

US State Department spokeswoman Amanda Batt confirmed the pair's arrest, although she did not name them, and pressed for "the immediate release of both detained persons", French news agency AFP reported.

The ELN is Colombia's largest left-wing guerrilla group after the Revolutionary Forces for Colombia, or FARC, and has about 3,500 members who specialise in kidnappings.

'In good health'

On Friday right-wing paramilitary group the United Self Defence Forces of Colombia (AUC) released three foreign nationals it had seized near the Panama border last Sunday.

Uribe has pledged to crack down on both left and right-wing rebels

American-Canadian journalist Robert Pelton and his two American companions, Megan Smaker and Mark Wedeven, were handed over to Catholic Church officials in the remote village of Unguia, about 280 miles (450km) northwest of Bogota.

Mr Pelton is best known as the author of the book "The World's Most Dangerous Places", a guide to global conflict zones.

All three were said to be in good health.

Colombian President Alvaro Uribe was elected last year on a promise to take a hard line against left-wing rebels and right-wing paramilitary groups. However, kidnappings and attacks by both sides have continued.