Rebels have vowed to kill the hostages if a rescue bid is staged

The visit is aimed at satisfying a key demand of left-wing rebels currently holding seven tourists hostage.

The rebels accuse right-wing paramilitaries of blockading villages in the area, denying residents food and medical supplies.

They want the allegations verified before releasing their hostages.

Village visit

United Nations representatives joined local human rights officials and church members to form the mission, which arrived in the Sierra Nevada mountains on Saturday.

"The inspection mission will hear from the communities about the situation of human rights, their situation of poverty and everything," Monseigneur Hector Fabio Henao told local television.

The mission - including for the first time UN representation - is scheduled to canvass the experiences of residents in at least six villages in the region.

The rebels, from the National Liberation Army (ELN), kidnapped eight foreign tourists near the ruins of the ancient Lost City on 12 September.

One of the hostages, Matthew Scott from the UK, made a daring escape and spent days trekking through the jungle without food before finding help.

But another Briton, four Israelis, a Spaniard and a German citizen remain captive, despite an expensive and wide-ranging search by Colombian authorities.

The ELN has said it will release the German woman and Spanish man on Monday, but has not set a date for the release of the remaining five hostages.

'Drinking whisky'

The conduct of right-wing paramilitaries has also come under scrutiny in another development, as the Colombian president criticised a police unit.

Alvaro Uribe accused officers of carousing with right-wing paramilitaries, who were then seen extorting protection money from local businesses in clear view of the police.

"The mayor tells me, the townspeople tell me, 'Look, the police don't leave town. And [outside] there are the guerrillas, and the police stay in town drinking whisky with the paramilitaries'," Mr Uribe said at community meeting in the city of Rionegro, in his home province of Antioquia.

"We cannot allow this," he said, according to news agency Reuters.

He called the subsequent collusion between the paramilitaries and police in the protection rackets "a mortal sin".

The paramilitaries - heavily suspected of wider collusion with Colombian authorities by some watchers - are also blamed for thousands of civilian deaths in the four-decade dirty war with rebels.