By Cheikh Diouara and John Irish

KIDAL, Mali/PARIS (Reuters) - Tuareg rebels in northern Mali said on Monday they had captured two senior Islamist insurgents fleeing French air strikes toward the Algerian border and France pressed ahead with its bombing campaign against al Qaeda's Saharan desert camps.

Pro-autonomy Tuareg MNLA rebels said one of their patrols seized Mohamed Moussa Ag Mohamed, an Islamist leader who imposed harsh sharia (Islamic law) in the desert town of Timbuktu, and Oumeini Ould Baba Akhmed, thought to be responsible for the kidnapping of a French hostage by al Qaeda splinter group MUJWA.

"We chased an Islamist convoy close to the frontier and arrested the two men the day before yesterday," Ibrahim Ag Assaleh, spokesman for the MNLA, told Reuters from Ouagadougou in Burkina Faso. "They have been questioned and sent to Kidal."

France has deployed nearly 4,000 ground troops, as well as warplanes and armored vehicles in its three-week-old Operation Serval that has broken the Islamist militants' 10-month grip on northern towns. It is now due to gradually hand over to a U.N.-backed African force of some 8,000 troops, known as AFISMA, of which around 3,800 have already been deployed.

Paris and its international partners want to prevent the Islamists from using Mali's vast desert north as a base to launch attacks on neighboring African countries and the West.

After meeting French President Francois Hollande in Paris, U.S. Vice President Joe Biden praised the "decisiveness and incredible competence" of France's operations. He backed France's call for U.N. peacekeepers to be deployed in Mali.

"We agreed on the need to, as quickly as reasonably possible, establish an African-led mission to Mali and, as quickly as is prudent, transition that mission to the United Nations," Biden said, flanked by Hollande.

Paris believes that deploying U.N. peacekeepers to Mali could eliminate problems over funding the African mission and fears of ethnic reprisals by Malian troops against light-skinned Tuaregs and Arabs associated with the Islamists.

BAMAKO HESITATES OVER TALKS

The MNLA, which seized control of northern Mali last year only to be pushed aside by better-armed Islamist groups, regained control of its northern stronghold of Kidal last week when Islamist fighters fled French air strikes into hideouts in the nearby desert and rugged Adrar des Ifoghas mountains.

The Tuareg group says it is willing to help the French-led mission by hunting down Islamists. It has offered to hold peace talks with the government in a bid to heal wounds between Mali's restive Saharan north and the black African-dominated south.

"Until there is a peace deal, we cannot hold national elections," Ag Assaleh said, referring to interim Malian President Dioncounda Traore's plan to hold polls on July 31.

Many in the southern capital Bamako - including army leaders who blame the MNLA for executing some of their troops at the Saharan town of Aguelhoc last year - strongly reject any talks.

"One of the first conditions for reconciliation is to disarm rebel groups," Malian Foreign Minister Tieman Hubert Coulibaly told Reuters in Paris. "We must first liberate the north of Mali and then we can organize elections."

French special forces took the airport in Kidal on Tuesday, reaching the most northern city previously held by the Islamist alliance. The French presence at the airport has since been reinforced by two parachute units.

Though the MNLA says it controls Kidal, France's defense ministry said on Monday that 1,800 Chadian troops - part of a U.N.-backed African mission sent to help retake northern Mali - had entered the city.

TARGETING REBEL BASES, DEPOTS

French Foreign Minister Laurent Fabius said warplanes were continuing bombing raids on Islamists in Mali's far north to destroy their supply lines and flush them out of remote areas.

"The objective is to destroy their support bases, their depots because they have taken refuge in the north and northeast of the country and can only stay there in the long-term if they have the means to sustain themselves," Fabius said. Continued...