The UK has agreed to help transport foreign troops and equipment to Mali amid French efforts to contain rebels.
In recent days France has attacked militants in Mali to support the Malian government, and has attempted to rescue a French hostage in Somalia.
Downing Street stressed no UK troops would be deployed in a combat role.
The move was agreed in a phone call between Prime Minister David Cameron and French President Francois Hollande, Downing Street said.
“The prime minister spoke to President Hollande this evening 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) will discuss the situation in Mali when it meets on Tuesday.
Meanwhile, President Hollande has ordered security is stepped up around French public buildings and transport following the operations in Mali and Somalia.
French troops were deployed in Mali on Friday after its army lost control of a strategically-important town to Islamists who were advancing south. The rebels took control of a huge swathe of northern Mali last April.
The central town of Konna has since been recaptured, the Malian government says.
Then, French commandos went into action in Somalia, swooping on the town of Bulo Marer in an attempt to free Denis Allex, who was kidnapped in July 2009.
A battle erupted with al-Shabab militants and, according to President Hollande, the operation failed “despite the sacrifice of two of our soldiers and probably the assassination of our hostage”.