(Adds Karzai comments)

By Elizabeth Pineau

KABUL, Aug 20 (Reuters) - President Nicolas Sarkozy said on Wednesday he did not regret sending 700 more troops to Afghanistan this year, after insurgents killed 10 French soldiers, the biggest single loss for foreign forces in Afghan combat since 2001.

The soldiers were killed in a major battle that erupted when Taliban insurgents ambushed a French patrol just 60 km (40 miles) east of the Afghan capital on Monday. The fighting has heightened fears the militants are gradually closing in on Kabul itself.

"The best way of remaining faithful to your comrades is to continue the work, to lift your heads, to be professional," Sarkozy told French troops at a base on the outskirts of Kabul. "I don't have any doubt about that. We have to be here."

Sarkozy sent an extra 700 troops to Afghanistan this year, responding to U.S. pleas for its NATO allies to do more to help check the resurgent Taliban. That brought the number of French troops in Afghanistan to about 2,600.

"I tell you in all conscience, if it had to be done again, I would do it," he said.

In a visit due to last just a few hours, Sarkozy first paid his respects to the dead soldiers. He then visited the 21 French soldiers wounded in the battle and held talks with Afghan President Hamid Karzai before leaving the country.

SANCTUARIES

Karzai said he was "tremendously saddened and shaken" by the deaths and expressed his condolences to the French people.

"The rise in violence is attributed directly to our lack of attention, the allies and all of us, to the sanctuaries, to the training grounds, to the financial resources, of terrorists and the Taliban," Karzai told reporters.

"Unless we do that we will continue to suffer," he said. Karzai and Afghan leaders accuse neighbouring Pakistan intelligence agents of backing the Taliban and Pakistan's government of allowing the militants sanctuary in the lawless tribal regions along the Afghan border.

Pakistan denies the charge and says insurgent violence in Afghanistan is an Afghan domestic issue.

Sarkozy was accompanied on the trip by Foreign Minister Bernard Kouchner, Defence Minister Herve Morin and the French armed forces chief, General Jean-Louis Georgelin.

Sarkozy said the work the troops were doing was vital.

"A part of the world's freedom is at stake here. This is where the fight against terrorism is being waged," he said. "We are not here against the Afghans. We are with the Afghans so as not to leave them alone in the face of barbarism."

The loss of 10 troops was the worst suffered by the French army in a single incident since 58 paratroops were killed by a suicide bomber in Lebanon in 1983 and the worst in combat with enemy forces since the Algerian war that ended in 1962.

It was also the worst single loss in combat for troops from NATO's International Security Assistance Force (ISAF) in Afghanistan since U.S.-led and Afghan forces toppled the Taliban in the wake of the Sept. 11, 2001 attacks on the United States.

Monday's ambush took to 24 the number of French soldiers killed in Afghanistan since 2002. (Writing by Jon Hemming; Editing by Roger Crabb and Valerie Lee)

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