A British explorer who went missing after being caught up in fighting during an attempt to reach a remote tribe in Papua New Guinea has reportedly been spotted "alive and well".

Benedict Allen is said to have been sighted near an airstrip and has requested rescue, according to local missionaries.

Mr Allen is understood to have been marooned near the airstrip after fighting between different tribes in the area cut off roads and bridges.

He had not been seen since being dropped by helicopter into the remote jungle three weeks ago without a mobile phone or GPS device.

Mr Allen was hoping to reach the Yaifo, a tribe thought to be one of the last on Earth to have no contact with the outside world.

His friend Frank Gardner, the BBC's Security Correspondent who travelled to Papua New Guinea with him twice last year, said Mr Allen had tracked "huge distances" to reach the remote airstrip.

Mr Gardner said: "Benedict Allen is not out of danger yet. He is currently marooned in a remote part of Papua New Guinea that is only reachable by air after all the road bridges were cut due to tribal fighting.

"Urgent efforts are now under way to try to airlift him out as soon as possible in case fighting erupts around him."