WASHINGTON (CNN) -- Insurgents who squared off with U.S. soldiers in a major battle in eastern Afghanistan overran a military observation point just outside a coalition outpost, but failed to take the base, a U.S. military official told CNN.
U.S.-led coalition, Afghan and NATO officials were attempting to piece together details about the confrontation which occurred Sunday in Kunar province, a location close to the Pakistan border.
"It was heroic fighting," said another official, NATO spokesman Mark Laity, describing the U.S.-led troop performance.
"They wanted to overrun that base," he added, referring to the militants. "They failed."
The fighting left nine U.S. soldiers dead and 15 wounded. It marked the most fatalities in an attack on U.S. troops in Afghanistan in three years. An Afghan official estimated that 100 militants died or were wounded in the fighting.
A U.S. official told CNN that as many as 200 insurgents were involved in the strike, which NATO said occurred at an outpost in Dara-I-Pech. However, other officials could not put a figure on the number of insurgent casualties at this time.
The official said militants didn't get into the outpost but they did overrun a small U.S.-led observation point outside the base, where it is believed most of the American and Afghan fatalities and injuries occurred. Watch more about the attack on the coalition base »
Laity described the insurgent strike as a "major attack" by a "large group of insurgents."
"What there was was a combat outpost had a major attack on it by a large group of insurgents. They had infiltrated a neighboring village and they fired on the base from that village and then they attacked the base itself."
He said severe fighting followed, resulting in the American casualties and the wounding of four Afghan service members.
"They attempted to break into that base. They did make some penetration. But overall they were repelled and they took very heavy casualties themselves," Laity said.
He indicated that the penetration or breach that media reports about the strike referred to was the attack on the observation post.
"We brought in air power to stabilize the situation in a fight that then lasted for several hours," he said.
There have been occasional strikes on coalition bases in recent months -- Laity noted that the practice "is quite common."
"This was a larger-scale attack than normal," he said, but added, "This was not a new tactic. They usually get defeated. We are very, very sad that we lost some people but again, their attempt to take that base failed."
Gen. Mohammad Zahir Azimi, an Afghan Defense Ministry official, had different initial numbers than the U.S. official. He said the attack involved 400 to 500 militants, and at least 100 were killed or injured, he said.
In June 2005, 16 U.S. troops were killed near the same province when their MH-47 helicopter was shot down by a rocket-propelled grenade.
Since the start of coalition operations in Afghanistan, 470 U.S. troops have died, including Sunday's casualties.
The battle illustrates the escalating war in Afghanistan, where since May U.S. and coalition troop deaths have exceeded those occurring in Iraq.
Many of the attacks against NATO-led and Afghan troops in southern and eastern Afghanistan are roadside bombs, and to confront that threat, U.S. military commanders have asked the Pentagon to send hundreds of MRAP armored vehicles, designed to withstand strong explosives, as quickly as possible to U.S. troops battling the Taliban.
Defense sources said the request could include between 600 and 1,000 MRAPs -- Mine Resistant Ambush Protected vehicles, many originally destined for Iraq but not needed there as much now because of the dramatic drop in violence there.
The MRAPs, which are the newest armored vehicles, have a V-shaped hull that helps deflect the blast of a roadside bomb.
The troops in the east have been quite busy and they are using all of the equipment they have on hand to conduct their fight, officials have said.
For example, when Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, was in the east's Korengal Valley recently, the helicopters that dropped him off at a base immediately left to join in a firefight on the other side of the valley.
--CNN's Barbara Starr contributed to this report