KANDAHAR, Afghanistan, May 5 (Reuters) - Afghanistan's Taliban has extended the Saturday deadline for a deal for the release of a kidnapped French aid worker until after presidential elections on Sunday in France, a spokesman said.

The Frenchman, known only as Eric, and his three Afghan colleagues would be freed if at least one of the Taliban's demands were met, spokesman Qari Mohammad Yousuf added.

The Taliban leadership council had extended the deadline as a sign of mercy, Yousuf told Reuters by phone from an undisclosed location, but had heard nothing from authorities seeking the release of the aid workers.

"Our reaction is clear, we may kill him," he said, when asked what the Taliban would do if none of its conditions were met.

The Taliban last month abducted two French aid workers and three Afghans working for Terre d'Enfance, an agency helping children in southwestern Afghanistan.

A French woman named Celine was released late last month in what the Taliban said was a humanitarian gesture.

The militants have demanded the withdrawal of French forces from Afghanistan and the release of jailed Taliban by the Afghan government, with a deadline of Saturday set for a deal.

President Hamid Karzai said this week efforts were under way to secure the release of the French man, after calls from French President Jacques Chirac for him to intervene.

The five were kidnapped in the southeastern province of Nimroz, sandwiched between Iran and Afghanistan's opium centre of Helmand.

Italian journalist Daniele Mastrogiacomo, who was kidnapped last month, was freed after two weeks when Kabul released five senior Taliban prisoners.

But his Afghan driver was beheaded in front of him before his release and his translator was later beheaded when the Afghan government refused to free more Taliban.

The Mastrogiacomo deal drew criticism in Afghanistan and Italy for encouraging the Taliban to take more hostages.

The Taliban are also holding five Afghan health workers and have threatened to kill one soon unless the government starts peace talks.

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