Maoist guerrillas have abducted two Italians on vacation in a remote district of India's Orissa state, marking a potential escalation of a decades-long rebel war considered India's most serious internal security threat.

"We have imprisoned two Italian tourists," Sabyasachi Panda, organizing secretary of the state committee of the outlawed Communist Party of India- Maoist, said in an audio message sent to local reporters and obtained by Reuters.

He said the tourists were seized after they were spotted taking photos of women from one of India's indigenous tribes who were bathing in a riverin the eastern state.

The Italian Foreign Ministry identified the abducted men as Paolo Bosusco and Claudio Colangelo. It said it was in contact with Indian police through its embassy.

Bosusco runs a travel agency called Orissa Adventurous Trekking and has been a regular visitor to India for the last 15 years, Italian media reported.

Indian Prime Minister Manmoham Singh has declared the longstanding rebellion the biggest single threat to internal security.

Hundreds die each year in violence linked to the insurgency but the guerrillas are not known for targeting foreigners.

At a news conference on Sunday, Orissa's home secretary UN Behera said the kidnapping took place on Saturday. Police say the tourists had been warned not to enter the area.

The Maoists say they are fighting for the rights of the poor and landless and stage ambushes in the swathe of eastern and central India in which they have a strong presence.

Panda gave a list of 13 demands to be met by Sunday to ensure the safety of the Italians, including the release of top Maoist leaders from prison and an end to counter-insurgency operations in the state.

The extremists abducted two officials last year, but released them a week later after the government agreed to meet their demands.

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The rebels draw recruits from tribal communities, which are often desperately poor and in areas where the state has little presence. Orissa this year promised to clamp down on travel agencies offering "human safaris" to remote tribal areas.

Tensions between India and Italy have been running high since Indian police arrested two Italian marines a month ago in the sourthern port of Kochi, accusing them of kiling two Indian fishermen. India has ignored repeated calls from the Italian government for the men to be released.