Insurgents killed nine U.S. soldiers in an assault on an Afghan army and NATO outpost in northeastern Afghanistan on Sunday, making it one of the worst days for foreign troops casualties in the country since 2001.

Afghanistan is suffering from a rising tide of violence this year, with a sharp increase in Taliban attacks, especially in the east where NATO says militants have taken advantage of peace deals in Pakistan to cross the border and fight in Afghanistan.

"The fighting began in the early morning hours and continued into the day as insurgents were repulsed from an Afghan National Army and ISAF combat outpost," a statement by the NATO-led International Security Assistance Force (ISAF) said.

The dead soldiers were all American, a NATO official said. Fifteen ISAF troops and four Afghan soldiers were also wounded in the fighting.

"Although no final assessment has been made, it is believed insurgents suffered heavy casualties during several hours of fighting," it said. The fighting took place in the northeastern province of Kunar, close to the border with Pakistan and also to neighbouring Nuristan province.

Afghan authorities said earlier in the day five Pakistani Taliban were killed and 13 more wounded after they infiltrated Nuristan province on Saturday. The Defence Ministry said dozens of insurgents were killed and dozens more wounded in a counter-attack by the Afghan army in Nuristan on Sunday.

ISAF said they had no record of any fighting in Nuristan on Sunday, so it was not clear whether Afghan authorities were referring to the same clashes which the NATO force said were in a nearby area of Kunar province.

RISING VIOLENCE

Separately on Sunday, a roadside bomb killed a U.S. coalition soldier in the southern province of Helmand. At least 40 militants were killed as Afghan and coalition troops returned fire and called in airstrikes, the U.S. military said in a statement.

Growing insecurity has added to the frustration of many Afghans more than six years after U.S.-led and Afghan forces overthrew the Taliban government after it refused to hand over al Qaeda leaders behind the September 11 attacks on the United States.

A Taliban suicide bomber killed at least 17 civilians, most of them children, and four police in a bazaar in southern Afghanistan on Sunday, police said.

Taliban suicide bombs have killed more than 230 civilians and wounded nearly 500 already this year, NATO says. While Afghan and foreign forces are stopping a greater proportion of the attacks, security experts say, the Taliban are attempting many more suicide bombings this year.

In the latest attack the bomber, travelling on a motorcycle, targeted a police vehicle in a bazaar in the Deh Rawood district of Uruzgan province, the provincial police chief told Reuters.

"Seventeen civilians and four policemen died in the attack. Thirty-seven more civilians and five police have been wounded," Juma Khan Himat said by telephone, adding the death toll could rise. Most of the civilian victims were children, he said.

The Interior Ministry in Kabul put the death toll higher. It said 24 people, four of them police, including a senior officer, were killed in the attack.