French President Francois Hollande announced on Friday that French forces have launched military intervention in support of Malian troops countering Islamist rebels' offensive.

"We are faced with a blatant aggression that is threatening Mali's very existence. France can not accept this," said the French head of state.

"I have decided that France will respond, together with our African partners, to the request from Malian authorities. We will do it strictly within the framework of a UN Security Council resolution," the president said, referring to motions adopted by the UN Security Council since the beginning of the crisis in Mali in March 2012.

Hollande's remarks came after Malian President Dioncounda Traore made a request to UN Security Council and Hollande, seeking for military aid from France countering the military movements and attacks by terrorist and extremist groups.

The UN Security Council had agreed last month to authorize the African-led International Support Mission in Mali (AFISMA), with 3,300 soldiers deployed, to support the African country in its fight against terrorists and armed rebel groups.

Latest reports showed that Mali's rebel groups had controlled the northern half of the country and are heading south. They have captured the strategic city of Konna, a central town of 50,000 people some 700 km northeast of capital Bamako, putting Mali sovereignty at risk.

The situation had caused UN's grave concern about the military movements of rebel groups along the frontline in northern Mali.

The Security Council met on Thursday, calling on member states to "assist the settlement of the crisis and, in particular, to provide assistance to the Malian Defense and Security Forces in order to reduce the threat posed by terrorist organizations and associated groups."

The French president said UN Security Council resolutions meant France's action is in accordance with international laws. He confirmed that the French troops' engagement in the military operation in Mali "will last as long as necessary."

Friday afternoon, French Foreign Ministry urged French nationals to leave its former colony, due to risks of escalating military tensions in the west African country.

French Foreign Minister Laurent Fabius said later Friday that French troops in Mali is aiming to help the country stop advance of terrorists. "We need to stop the advance of terrorists, otherwise Mali will falls in their hands," Fabius told journalists at a press conference.

The minister said that Paris military commitment to help quash Islamist rebels in Malian territory will help to release French hostages kidnapped in the Sahel region where seven French nationals are already in the hands of kidnappers.

"We must have in mind that the abductors are the same groups who move to south Mali, thus preventing them and responding with an extremely firm way we are serving the same cause : release of hostages," French top diplomat told reporters.

"The hostages have been since long months in an extremely dangerous situation... We will do everything to save them," he added.

The minister also confirmed that French air force carried out an air strike in Mali on Friday in support of government forces, but did not give further details.

Situation in Mali has deteriorated in the last few days, the minister warned. "Due to the delay between the taking of international decisions and their application, the terrorist and criminal groups moved south, their goal is to gain control of all of Mali and install in Mali a terrorist state," Fabius said.

Reports say Malian government forces launched on Friday an offensive against Islamist rebels and recaptured the central towns of Konna and Douentza with French and other foreign military support.