Lightning may have struck missing balloonists' craft
Two missing gas balloonists are either in a life raft somewhere or their balloon was hit by lightning and exploded, their ground crew have said.
Americans Richard Abruzzo and Carol Rymer Davis went missing in thunderstorms over the Adriatic.
The pair were taking part in the Gordon Bennett Cup race which launched from near Bristol on Saturday.
A search led by the Italian Maritime Rescue Co-ordination Centre (MRCC) has been going on since Wednesday.
A vigil has been held for the missing balloonists in America where they were described as "true adventurers" and friends said they were "still hoping for the best".
Rob Bayly, a member of the Abruzzo-Davis retrieve crew, described two possible scenarios.
He said: "The good news story is that they managed a rather desperate water landing, ejected from the balloon and are in a life raft somewhere, yet to be found, and the balloon took off without them with their beacon still on board, therefore not yet triggered.
"The other very pessimistic scenario is a catastrophic explosion in the air where they were caught in the thunder storms, very, very, violent updraughts and downdraughts, and of course lightning itself could have struck the balloon which - at many thousands of feet - could have been completely destroyed."
The MRCC has been searching for the pair using four boats, an aircraft and a helicopter, supported by the US military and Croatian and Greek search and rescue authorities.
The event's control centre in Bristol is providing technical details to the Italian coastguard to aid the search.
'Well-prepared and experienced'
A statement from the centre said: "The Italian MRCC has been extremely thorough in their operations, but unfortunately all items found have not been related to the search."
Family friend of Richard Abruzzo, The mayor of Albuquerque, Richard Berry, said: "These are true adventurers. These are people who dedicate and risk their lives to do what they love in the sport that they love.
"I went to university with Richard and he and his family are well known and really are true leaders in our community.
"Richard has been ballooning for all of his life and I've a lot of confidence he and Carol Rymer Davis are well-prepared and experienced and we are still hoping for the best."
The Italian coastguard last had contact with the pair, who won the race in 2004, at 0800 local time (0700 BST) on Wednesday when they reported bad weather conditions.
The 19 other balloons taking part in the race had landed safely by Wednesday.
The last satellite tracker report from the missing balloon - USA2 - was at 0658 BST.