An ambush that killed two American servicemen is a sign rebel activity is increasing in Afghanistan following the start of the war in Iraq, an Army spokesman said.

Col. Roger King also said Sunday that the military was considering new offensives in the area of southern Afghanistan where the ambush occurred.

"This helps paint the picture for future operations," King told reporters. However, he said, the attack also "points out that it's a challenge to pick out enemy forces that are made up of local Afghans."

Late Sunday, a rocket hit the headquarters of the international peacekeeping force that patrols Kabul, the Afghan capital. No injuries were reported.

Afghan authorities say Taliban, their Al Qaeda allies and forces loyal to a renegade rebel commander are behind the killings and the rocket attacks.

Saturday's attack in the southern province of Helmand was the first fatal encounter for U.S. forces in Afghanistan since December.

A Special Forces soldier and an airman were killed and another Special Forces trooper wounded when their four-vehicle convoy was ambushed on a reconnaissance patrol. Three Afghan soldiers also were wounded.

The Americans killed were identified by authorities and family members as Army Special Forces Sgt. Orlando Morales, 33, of Manati, Puerto Rico and Staff Sgt. Jacob L. Frazier, 24, a member of the Illinois Air National Guard from St. Charles, Ill.

The attack occurred two days after an international Red Cross worker was killed in neighboring Kandahar province. The region is the birthplace of the hardline Taliban regime driven from power by American-led forces in late 2001.

King said it was not clear whether there was any connection between the two attacks. U.S. forces and Afghan militia have been conducting sweeps in Kandahar province -- and such offensives often spur more rebel activity.

"If we take aggressive, offensive actions, oftentimes we get a reaction from the enemy forces," King said at Bagram Air Base, the headquarters of the U.S.-led coalition.

Hundreds of coalition forces swept into the Helmand Valley last month for Operation Viper, and patrols of the perilous area continue. The ambush "probably will point to the fact that we need to conduct more operations in the area," King said.

The ambush was part of an "uptick" in rebel activity following the start of the Iraq war about 10 days ago, he said. Anti-U.S. forces had vowed to step up attacks if war against Saddam Hussein erupted.

The attack raised to 28 the number of combat deaths among the coalition forces in Afghanistan, King said. Another 34 have died in accidents or from other causes.

On Thursday, gunmen shot to death a Red Cross water engineer on a dirt road in neighboring Kandahar province, the first foreign aid worker killed since the Taliban fell. The International Committee of the Red Cross curtailed operations in Afghanistan, its largest relief effort.

"I am struck by what this shows about the enemy," King said of Thursday's attack. "It shows enemy forces have zero regard for the population of Afghanistan. The only people they're hurting in attacks like this are the Afghan population."

In a joint U.S.-Afghan military operation against the Taliban in the Kandahar area, eight rebels were killed and 13 captured in two days of fighting, including a suspected senior Taliban leader, said Khalid Pashtoon, a spokesman for the provincial governor of Kandahar.

Last week, U.S. forces wrapped up Operation Valiant Strike in the Sami Ghar mountains in Kandahar province, and blew up several weapons caches, although they did not come upon any enemy fighters.

The rocket that hit the peacekeepers' compound on Sunday was one of two to strike Kabul. The second hit the Pul-e-Charkhi area, on the eastern edge of the capital. There were no reports of injuries there either.

Peacekeepers have stepped up patrols of Kabul since a Dutch soldier was wounded three weeks ago in a mine blast, a spokesman said. The Dutch peacekeeper's translator was killed.

German Lt. Col. Thomas Lobbering, spokesman for the 5,000-strong force, said forces loyal to renegade rebel leader Gulbuddin Hekmatyar -- a suspected ally of the Taliban -- have been "reorganizing" for several months.

"To our judgment, they are not capable of reorganizing themselves in any military sense, but they are capable to commit terrorist attacks, suicide attacks, grenade attacks," Lobbering told The Associated Press.