Mali: No UK army boots on the ground - Cameron
The prime minister has restated that British troops will not go on to the ground in Mali, despite the UK offering logistical support to France.
Two RAF C17 cargo planes are helping French military efforts against Islamist rebels. The first is delayed in France due to technical issues.
David Cameron said the French action in Mali was "in our interests" and should be supported.
France has attacked the militants since Friday, to support Mali's government.
Its armed forces have been helping government forces in the West African country recapture the central town of Konna.
France has called a meeting of the UN Security Council to discuss the situation in Mali on Monday.
French President Francois Hollande has argued that Mali could become a "terrorist state" that could threaten the rest of Africa and Europe if the rebel advance is not halted.
Defence minister Andrew Robathan told the Commons the UK's commitment of two RAF planes to assist French military operations was planned to last a week.
The first of the two C17s left RAF Brize Norton in Oxfordshire on Sunday and was loaded with French armoured vehicles and other equipment at the Evreux airbase in Normandy overnight.
It was due to fly to Mali's capital, Bamako, on Monday morning, but has been delayed due to a "minor technical fault", an MoD spokesman said.
The problem is thought to be a short-term one and the plane is expected to be ready to depart later.
A second C17 has now arrived at the French airbase and is expected to be the first to leave for Mali once it is loaded.
Mr Cameron told BBC Radio 4's Today programme Britain would also share intelligence with France as part of its campaign.
"There is a very dangerous Islamist regime allied to al-Qaeda 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," he said.
"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 Minister for Africa, Mark Simmonds is expected to update MPs on the UK's role in the operation in an oral Commons statement on Monday afternoon.
The government's National Security Council is set to discuss the situation in Mali when it meets on Tuesday.
The European Union has said it would bring forward a military training mission to Mali, which would be launched "in the second half of February or early March".
In December, the EU said it would train Malian and other African troops before they tried to retake the north from rebels, but the spokesman said that ongoing fighting made the mission more urgent.
Asked whether the UK would play any part in the training, the prime minister's official spokesman told reporters: "We are discussing that training mission with our European partners."
The French are trying to halt an advance by rebels affiliated with al-Qaeda, who have been pushing south from their northern base against the Mali government.
They deployed 550 troops last week after Mali forces lost control of the strategically important town of Konna to the rebels.
The town has since been recaptured by Malian troops with French aerial support.
Islamist groups and secular Tuareg rebels seized a swathe of northern Mali in April 2012 after taking advantage of chaos following a military coup.
On Monday, Islamists took the town of Diabaly, 400km (250 miles) from Bamako, in a counter-attack, French Defence Minister Jean-Yves Le Drian said.
He said Islamists had retreated in the east, but said French forces were facing a "difficult" situation against well-armed rebels in western areas.
The BBC's Hugh Schofield in Paris said the fallout from the action was potentially enormous for French President Francois Hollande.
He says the consequences ranged from the risks of military mission creep, to the strategic repercussions on France's relations in Africa, to the very real threat of terrorist reprisals on hostages and in France.