Six rescued British cavers at the centre of a political dispute were detained and questioned by Mexican immigration officials last night and President Vicente Fox said he was not satisfied with Britain's explanation of their activities.

A day after the explorers, most of them military, were pulled from a flooded cavern, the cavers and seven colleagues were taken to an immigration office, in the capital Mexico City, where they were questioned for several hours about possible violations of their immigration status.

President Fox told a news conference in Nicaragua that his government had asked Britain for "clear information about what they were doing".

He said the British Government had responded, "but frankly it did not satisfy. We want more clarity about what this affair is about".

British defence chiefs insisted the potholers were engaged in nothing more than adventure training.

A rescue team reached the party and used scuba gear to guide them back above ground after they were trapped by rising water in the Cueva Alpazat caves, north- east of Mexico City, on Wednesday last week.

All the men, including civilian Simon Cornhill, from Ripon, North Yorkshire, were said to be in good spirits as they were taken for medical checks at a hospital in nearby Peubla.

Yesterday, one of the potholers, retired Army major Jonathan Sims, said the party was never in any danger.

Other military personnel in the team included Warrant Officer Sergeant Charles Milton of the Royal Navy, Army Sergeant Chris Mitchell, John Roe of the RAF, and Tony Hamnett. Experienced caver Mr Cornhill was believed to have been assisting the group.

Last night, the Ministry of Defence declined to give any further information about the men or where they are usually based.