NATO released Thursday the first details on an insurgent attack that killed five U.S. soldiers over the weekend, saying the Americans were trying to rout militants from a volatile valley in eastern Kunar province when they came under fire.

The area along Afghanistan's eastern border with Pakistan has continued to see heavy fighting as NATO focuses most of its efforts on a troop surge in the south aimed at breaking Taliban strongholds there.

Also Thursday, NATO announced two more deaths in the south — one from a bomb explosion and the other in an insurgent attack. The military alliance said both soldiers died Wednesday but did not provide details or disclose their nationalities.

Thirty-nine NATO service members have been killed so far this month in Afghanistan, including at least 33 Americans.

The five American soldiers who died Sunday were "conducting clearing operations" when they came under fire in Watapur valley, said Master Sgt. Brian Sipp, a spokesman for the international military alliance.

Sipp did not say how many troops were involved in the fight, nor provide an estimate of the number of attackers. The fighting started around 2 p.m. and lasted at least six hours, he said, with the wounded and the killed not being evacuated until late that evening.

Another American soldier died in the area Tuesday when insurgents fired on his unit, according to the military.

All six deaths occurred during a four-day push called Operation Bulldog Bite to search out militants and weapons caches near the Pech river.

The area has long been a transit route for insurgents coming over from the Pakistan border and has proved a tricky area for U.S. forces trying to secure the mountainous terrain and coax villagers away from supporting the insurgents and criminals who control much of the area.

Watapur is just 5 miles (8 kilometers) from the Korengal valley, where U.S. troops ceased operations seven months ago, saying that it was not strategically important. Forty-two Americans died in Korengal before the troops pulled out.

Operation Bulldog Bite has killed at least five insurgents, though there have been unconfirmed reports of as many as 49 insurgents killed, said Maj. Mary Constantino, a spokeswoman for U.S. forces in the area.

In addition, the forces found weapons caches containing mortar systems with rounds, more than a dozen rocket-propelled grenades, 20 anti-aircraft rounds

"Operation Bulldog Bite has degraded the insurgents' ability to terrorize the people of the Pech valley," Constantino said.

Three Afghan soldiers were also killed in the operation, said Gen. Khalilullah Zaiyi, the Kunar province police chief. He said about 30 insurgents were killed.