Military source says number of forces will eventually grow to 2,500

A contingent of 750 French troops has joined the offensive against Islamist rebels in Mali, French President Francois Hollande said in Abu Dhabi on Tuesday after France secured fresh UN backing for its military action.

Hollande, who arrived early on Tuesday in the United Arab Emirates, added that overnight strikes in Mali had "achieved their objective".

"For now, we have 750 men and the number will increase," Hollande said during a visit to his country's only military base in the region - Peace Camp in Abu Dhabi.

France's intervention force in Mali will gradually increase to 2,500, said a source close to Defense Minister Jean-Yves Le Drian.

The 750 French troops in Mali are backed up by Rafale fighters and helicopters.

But the plans to deploy a force of that size is at odds with suggestions by government ministers that the involvement of French ground troops would be limited to protecting Mali's capital, Bamako.

A meeting of the 15-nation UN Security Council on Mali expressed unanimous "understanding and support" for the military intervention, France's UN Ambassador Gerard Araud said late on Monday.

But the Organization of Islamic Cooperation, of which Mali is a member, called on Tuesday for an "immediate" cease-fire, calling the offensive "premature" and urging all parties to return to the negotiating table.

The conflict in Mali has caused nearly 150,000 people to flee the country, while another 230,000 have been internally displaced, the UN humanitarian agency said on Tuesday.

France's top security official said the country is ready to prevent new terror attacks after its military operation to push back al-Qaida-linked insurgents grabbing territory in Mali.

Interior Minister Manuel Valls said on Tuesday that France is well aware of the dangers of terror attacks inside and outside France, but he believes the threat posed by the advance of the militant Islamist fighters was far greater.

Declaring France had "opened the gates of hell" with its assault, the rebels from the Sahel desert region that includes Mali threatened retribution on Monday.

A leader of the Movement for Oneness and Jihad in West Africa vowed revenge. "France has attacked Islam. We will strike at the heart of France," Abou Dardar of the al-Qaida-linked group said on Monday.

"France is watching individuals who want to go to Afghanistan, Syria and the Sahel. We're watching those who could return here," Valls told the French television network BFM. "We're facing an exterior enemy and an interior enemy."

Though driven from their strongholds by French Rafale fighter jets, the Islamists struck back on Monday in the government-held south, capturing the small town of Diabaly, some 400 km north of Bamako.

French planes hit Diabaly overnight, killing at least five Islamists, according to a security source. A resident said he saw armed Islamists fleeing after the strikes.

"They bombed Diabaly. They bombed the town all night long. I am hiding inside a house," said Ibrahim Toure, who was passing through Diabaly on his way to visit relatives when he got caught in the town. "It only stopped this morning, at around 6 am."

The France-led military intervention in Mali may last a few weeks, Malian Foreign Affairs Minister Tieman Hubert Coulibali said on Tuesday, adding that further military aid will be needed after the operation ends to help local authorities restore political stability.

AFP-AP-Xinhua