David Cameron has agreed to help transport foreign troops and equipment to Mali amid efforts to halt an advance by Islamist rebels in a conflict that has already claimed 120 lives.
The help was agreed in a phone call between the British prime minister and President Francois Hollande, after France sent in forces to support the Malian government.
French combat troops preparing to be airlifted into Mali on Saturday
Downing Street stressed that no UK troops would engage in combat operations in the country, but two transport planes, believed to be C-17s, are expected to be deployed within 24-48 hours.
"The Prime Minister spoke to President Hollande this evening [Saturday] to discuss the deteriorating situation in Mali and how the UK can support French military assistance provided to the Malian Government to contain rebel and extremist groups in the north of the country," a spokeswoman said.
"The Prime Minister has agreed that the UK will provide logistical military assistance to help transport foreign troops and equipment quickly to Mali.
"We will not be deploying any British personnel in a combat role. They also agreed that the peacekeeping mission from West African countries needs to be strongly supported by countries in the region and deployed as quickly as possible.
"Both leaders agreed that the situation in Mali poses a real threat to international security given terrorist activity there."
The Government's National Security Council (NSC) is set to discuss the situation in Mali when it meets on Tuesday.
Hundreds of French troops were deployed in Mali on Saturday after state forces lost control of a strategically important town to al-Qaida-linked Islamists. The rebels seized a swathe of northern Mali last spring.
France insists its soldiers have been deployed to aid West African troops, backed by the UN, in the fight against the rebels.
Washington is currently pondering whether to join France and Britain in aiding local troops via intelligence sharing against the rebels.
Britain is to send two C-17 transport planes to Mali
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.
Earlier, Cameron released a statement expressing "deep concern" about the rebel advances.
"I welcome the military assistance France has provided to the Malian government, at their request, to halt this advance," he said.
"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."
The Government's National Security Council (NSC) is set to discuss the situation in Mali when it meets on Tuesday.
The statement from No.10:
I am deeply concerned about the recent rebel advances in Mali, which extend the reach of terrorist groups and threaten the stability of the country and the wider region. 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. Last night’s tragic events underline how essential it is that we work together to combat terrorism in Africa.