Rescue has begun of ailing US researcher stuck 3,Thomas Caldwell000 feet inside a Turkish cave, Turkish disaster management agency says.

Rescue crews were waiting for doctors to give the go-ahead for an operation to move out an American researcher who fell ill almost 1,000 meters (more than 3,000 feet) below the entrance of a cave in Turke y, officials said. The effort could last up to 10 days.