(Adds Afghan army retakes districts in west and north)

By Hamid Shalizi

KABUL, Nov 10 (Reuters) - Taliban insurgents killed six troops from the NATO-led International Security Assistance Force (ISAF) and three Afghan soldiers in an ambush in eastern Afghanistan, an ISAF spokesman said on Saturday.

It was the heaviest loss suffered by ISAF troops in Afghanistan in three months and comes as Afghan and international troops are engaged in daily battles across the length and breadth of the country to contain the spreading Taliban insurgency.

"I have sad news to report from regional command east where six ISAF soldiers and three Afghan army were killed by Taliban insurgents in an ambush yesterday," Brigadier General Carlos Branco told a news conference in the Afghan capital, Kabul.

Eight ISAF troops and 11 Afghan soldiers were also wounded in the fighting, which began on Friday when insurgents ambushed their patrol with rocket-propelled grenades and small arms fire as the troops were returning from a meeting with local elders.

Most ISAF troops based in the east of the country are American, but the force is withholding confirmation of the nationalities of the dead soldiers pending notification of next of kin.

Elsewhere, a suicide bomber killed one civilian and wounded three other people in the northern province of Kunduz on Saturday, a provincial security official said.

FOREIGN FIGHTERS

In the west of the country, Afghan troops backed by ISAF soldiers retook the district of Gulistan, captured by the Taliban nearly two weeks ago, the Afghan Defence Ministry said.

A number of Taliban, including a commander, were killed in the fighting and the rest of the insurgents have fled to the mountains, the ministry said in a statement.

The Taliban capture of Gulistan was a rare rebel attempt to take and hold territory -- the insurgents prefer "shoot-and-scoot" tactics knowing that if they stay in one place for too long, air power can be brought into play against them.

Some 20 Taliban were killed or wounded and another 20 detained around Gulistan, the provincial police chief said.

Foreign fighters were helping the Taliban, he said.

"We have credible intelligence that Iranians and Pakistanis are fighting alongside the Taliban insurgents," Farah police chief Abdul Rahman Sarjang told Reuters. "We have also captured a large amount of brand new Iranian-made ammunition recently smuggled to Afghanistan," he said.

Afghan and Western officials have often said Taliban ranks are reinforced with foreign fighters, but say they have no proof of any official assistance, only that it is hard to conceive that Iranian arms made it to Afghanistan without the knowledge of Tehran's military.

In the northwest, the Afghan army said it had killed or wounded 50 Taliban insurgents, captured 20 more and forced the rest to flee an area straddling the border of Faryab and Badghis provinces where rebels had been interrupting aid to the region.

Violence in Afghanistan has steadily escalated since the Taliban relaunched their insurgency two years ago. More than 6,000 people have been killed since then.

Through their campaign of guerrilla tactics and suicide and roadside bomb attacks, the Taliban aim to convince ordinary Afghans their government and the more than 50,000 foreign troops in the country cannot bring security. (Additional reporting by Sharifuddin Sharafiyar in Herat and Tahir Qadiry in Maza-i-Sharif; Writing by Jon Hemming; Editing by Philippa Fletcher)

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