The pilots of at least 20 aircraft taking part in a vintage plane rally have been detained in Ethiopia, officials have told the BBC.
The Vintage Air Rally planes crossed "illegally" into Ethiopian from Sudan, officials say, and are currently impounded at an airport in Gambela.
The rally has been suspended while talks take place to try to resolve the situation.
Earlier, a UK pilot who went missing during the rally was found safe.
On its Facebook page, Vintage Air Rally said that Maurice Kirk, 72, was with other pilots in Gambela who were all "safe and accounted for".
The planes, dating from the 1920s and 1930s, took off from the Greek island of Crete on 12 November on a 13,000km (8,000 mile) journey to Cape Town.
However, the head of Ethiopia’s civil aviation authority, Wosenyele Hungnall, told the BBC that the aircraft had crossed illegally into Ethiopian airspace from Sudan.
He said the pilots had been detained and investigators were travelling to the area.
It is understood that those detained have had to surrender their mobile phones and other equipment, so details are unclear.
A rally spokesman told AFP news agency the problem may relate to landing permits, although he believed that all flight paths had been approved beforehand.
The aviators are being accommodated at Gambela airport, the rally said, instead of at a hotel where they had made bookings.
The UK’s foreign and commonwealth office (FCO) is among several foreign diplomatic services now involved in the situation.
An FCO spokeswoman said: "We are in contact with the local authorities regarding a group who have been prevented from leaving Gambela airport, Ethiopia."
A search and rescue operation was launched for Mr Kirk, from Somerset, after his aircraft went missing on Monday somewhere between Sudan and Ethiopia.
Rally organisers later confirmed that he was safe. They said that he had been asked to withdraw from the event because of a lack of satellite tracking or a working compass on his 1943 Piper Cub plane.
Mr Kirk, a former friend of the late actor Oliver Reed, previously reported suffering two engine failures, but had apparently decided to continue.