A United Nations aircraft has disappeared in central Angola with four crew members and ten passengers aboard, most of them members of the UN's observer mission in Angola.

Details are sketchy, but the plane is thought to have crashed.

One report said the it burst into flames shortly after take-off from Huambo on Saturday.

There's no indication whether it was an accident, or the plane got caught up in the renewed fighting between Angolan government troops and UNITA rebels.

The UN Secretary General, Kofi Annan, has appealed to the warring factions to help UN observers reach the crash site.

The BBC correspondent in Angola says the area is extremely dangerous: apart from the continuing clashes, it's also littered with landmines.