Afghan soldier on the run after killing 3 Gurkhas

KABUL (Reuters) - A renegade Afghan soldier is on the run after killing three British Gurkha soldiers in the Taliban's heartland, testing the trust of foreign and local troops fighting together as the war intensifies.

Afghan soldiers are expected to take more responsibility for the country's security as the 150,000-strong, U.S.-dominated force starts a gradual withdrawal from next year, and NATO commanders are quick to play up their role in joint operations.

The rapid creation of a national army and police force since the Taliban's ousting in 2001 and following decades of war has seen tens of thousands of Afghans join the security services, and there are fears Taliban insurgents -- or sympathizers at least -- may also have signed up.

Afghan authorities said last year they were tightening vetting procedures after a similar incident when a rogue soldier killed five British troops.

Although full details were not immediately available, ISAF officials said the three Gurkhas were killed in Helmand on Tuesday "in a suspected premeditated attack by a member of the Afghan National Army using a combination of weapons."

"We believe these were the actions of a lone individual who has betrayed his ISAF and Afghan comrades," said Lt.-Col. James Carr-Smith, a spokesman for Task Force Helmand, in a statement.

The seriousness of the incident prompted reaction from top military commanders and politicians in Afghanistan and abroad, who were all quick to stress unity.

"We must not let this change our strategy," said British Prime Minister David Cameron. "We need to make sure that we build up that army because that in the end is the way that we are going to be able to bring our troops back home."

"We have sacrificed greatly together, and we must ensure that the trust between our forces remains solid in order to defeat our common enemies," said General David Petraeus, recently appointed commander of NATO and U.S. forces.

Afghan President Hamid Karzai was upset and had called for a full investigation, an aide said, while Sher Mohammad Karimi, the army chief of staff, said the incident affected everyone deeply.

Regardless of the statements on unity from commanders and politicians, the incident will be keenly felt on patrols and at remote outposts where Afghan soldiers and foreign troops serve shoulder-to-shoulder, armed to the teeth.

"In that patrol base, this will be a traumatic event," Lt.-Gen. Nick Parker, deputy commander of ISAF and the senior British officer in Afghanistan, said in a statement.

The Gurkhas have played a significant role in British military history. Drawn from tough Nepali tribesman, they have a reputation for ferocity sharpened by stories of the curved Kukri dagger they all carry and must "blood" if ever drawn.

Foreign troops have also been responsible for many "friendly fire" incidents, the latest last week when five government soldiers died in a helicopter strike, prompting condemnation from the government.

There have also been several other attacks by insurgents in stolen army and police uniforms against government and international forces.

(Additional reporting by Ismail Sameem in Kandahar; Editing by Rob Taylor and XYZ)

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