LONDON, Aug 28 (Reuters) - Mokhtar Belmokhtar, a founder of al Qaeda's North African offshoot, is alive and leading military operations, an associate said on Tuesday, denying a report that the Algerian had been killed in clashes in Mali in late June.

Nicknamed the "uncatchable", Belmokhtar is believed to be linked to the kidnappings of foreigners that have taken place in remote areas of Africa's Sahel region in recent years.

He has been sentenced by an Algerian court to life imprisonment in absentia in connection with the killing of 10 Algerian customs agents in 2007.

Regional and Western governments fear that desert northern Mali could become the next launchpad for international Islamist attacks, as Afghanistan was more than a decade ago, and efforts are under way to organise a joint intervention force.

Ennahar TV, a private Algerian channel, quoted unidentified sources on June 28 as confirming Belmokhtar's death in armed clashes in the town of Gao.

But Oumar Ould Hamaha, a colleague of Belmokhtar's reached by telephone, said Belmokhtar was in good health.

"He is alive and fine, he is with us and he is moving around," Ould Hamaha said. "He is leading operations."

There was no independent corroboration of Ould Hamaha's comments, but a European official who follows North African armed groups said in early July that the Algerian television report was not regarded as reliable.

Belmokhtar heads one of two AQIM battalions in Algeria's southern desert bordering Mali.

The situation in northern Mali is chaotic after months of tension between the secular Tuareg-led National Movement for the Liberation of Azawad (MNLA) and better-armed local Islamists who helped it take control of the northern two-thirds of Mali in April but whose goal is to impose Islamic law.

Ennahar had said Belmokhtar was believed to have died during a battle in which at least 20 people were killed on June 27 in the north Mali town of Gao, where the Islamists had seized the MNLA headquarters, the source said. The Islamists have since declared they are in control of northern Mali.