The United States on Tuesday threw its support behind the French military action launched with the Malian government against rebels in the north of the country.

"It's absolutely critical to stop the offensive of terrorist groups towards southern Mali, to prevent the collapse of the government, and to accelerate the implementation of the UN Security Council resolutions on Mali," State Department spokeswoman Victoria Nuland said.

"So, it's in that context that the US very much welcomes the French military action in Mali," she told journalists.

A five-day old French military offensive in the West African nation has uprooted Islamist insurgents from several key strongholds as they sought to push an offensive south towards the capital, Bamako.

France is said to be planning to triple its force from a current 750 to a total of 2,500 troops, a sign that Paris is preparing for a drawn-out campaign to stem the advance of jihadists who have held northern Mali since April.

The first troops from a regional West African force were also bound for Mali on Tuesday to shore up the French and Malian government action.

Washington was already providing intelligence to the French at their request, and was now studying a request to help Paris airlift its troops into the country as well as aerial refueling help, Nuland said.

"We are looking hard today at the airlift question, helping them transport forces from France and from the area into the theater," she said.

Washington had also been in touch with a number of countries which make up the 15-nation Economic Community of West African States to accelerate the deployment of a UN-approved African-led force for Mali.

White House spokesman Jay Carney stressed however there were no current plans to send American troops into harm's way in Mali.

"We're not contemplating that kind of action, we're talking about logistical support, providing intelligence assistance," he said.

The administration of US President Barack Obama is financing the measures through some existing funding, but was also planning to ask Congress to unleash more money in the current days to support the ECOWAS plans.

Mali also topped the agenda Tuesday at talks here between visiting Liberian President Ellen Johnson Sirleaf and Secretary of State Hillary Clinton.

"The secretary did outline the support that we are prepared to offer to ECOWAS countries, as she did make clear that we support the French forces and that we are looking at how best to respond to the requests," Nuland said.