A British military aircraft bound for Mali to support French efforts against insurgents allied to al-Qaeda has been grounded due to a technical fault.
Despite being hailed by David Cameron "our most advanced and capable transport plane", the C-17 loaded with military equipment and troops has been delayed on its way to the west African country.
The huge four-engine jet can carry large equipment, supplies and troops directly to small airfields and is known for its robustness and capabilities for travelling long distances.
The problem is thought to be a short-term one and the plane is expected to be ready to depart later today, a Ministry of Defence spokesman added.
Britain is to send two C-17 transport planes to Mali
Mr Cameron told BBC Radio 4's Today that Britain would also share intelligence with France as part of its efforts to tackle the "dangerous Islamist regime".
"I spoke to (French president) Francois Hollande over the weekend and offered the use of two C-17 transport planes - our most advanced and capable transport planes - because France is a strong ally and friend of Britain but (also because) what is being done in Mali is very much in our interests," he said.
"There is a very dangerous Islamist regime allied to al Qaida in control of the north of that country. It was threatening the south of that country and we should support the action that the French have taken.
"So we were first out of the blocks, as it were, to say to the French 'We'll help you, we'll work with you and we'll share what intelligence we have with you and try to help you with what you are doing'."
The second plane was due to set off from RAF Brize Norton this morning for France, before continuing on to Mali.
French combat troops preparing to be airlifted into Mali on Saturday
French Rafale jetfighter landing after a mission to Mali in N'Djamena
Downing Street has stressed that no UK troops will engage in combat operations there, but the transport planes will provide logistical assistance.
Mr Cameron and President Hollande have agreed that the situation in Mali poses a real threat to international security, given terrorist activity there.
Hundreds of French troops were deployed on Saturday after state forces lost control of the strategically important town of Konna to Islamists last Thursday. The rebels seized a swathe of northern Mali last spring.
President Hollande also sent French commandos into Somalia in a failed attempt to rescue hostage Denis Allex, who was kidnapped in July 2009. Two soldiers and Mr Allex are believed to have died in the bid.
Paris insists the two operations are entirely separate. The country's terrorist threat level has been raised over fears of reprisals from extremists.
Mr Cameron has expressed "deep concern" about the rebel advances, saying: "I welcome the military assistance France has provided to the Malian government, at their request, to halt this advance.
"These developments show the need to make urgent progress in implementing UN Security Council resolutions on Mali, and ensure that military intervention is reinforced by an inclusive political process leading to elections and a return to full civilian rule.
"I would also like to send personal condolences to the families of the French hostage killed in Somalia and those of the two soldiers either killed or missing in the rescue attempt."
Africa Minister Mark Simmonds has indicated that British personnel could play a role in training the Malian army in addition to the logistical support already announced.
He is expected to update MPs on the UK's role in the operation in an oral Commons statement later this afternoon.
The government's National Security Council (NSC) is also set to discuss the situation in Mali when it meets tomorrow.