U.S. troops seized a large cache of weapons, including hundreds of mortars, rockets and land mines, and detained four suspects on Saturday during a sweep in southern Afghanistan, an official said.

The cache was found inside several buildings in a walled compound near the southern Sami Ghar mountains, where hundreds of U.S.-led troops are hunting for terror suspects in a broad new operation, said Lt. Col. Michael Shields, a senior operations officer of the coalition task force.

"To put it in perspective, we're still counting," Shields said, calling it the largest find in months. "In recent history, the size of this is significant."

The seizure came as suspected Taliban and Hizb-e-Islami renegades killed three Afghan soldiers at a post elsewhere in the southern Kandahar province.

The soldiers were trudging through the muddy, rugged terrain to pursue intelligence about other suspected weapons caches in nearby caves and mountains, he said.

The troops also arrested two suspected rebels near the weapons cache, Shields said, though he declined to provide further details.

The cache included hundreds of rocket-propelled grenade launchers and rounds, high-caliber machine guns, mortar rounds, anti-tank and anti-personnel mines and "too much ammunition of all caliber to count currently," Shields said.

Operation Valiant Strike — the latest U.S. offensive in the war on terror in Afghanistan — is being conducted in villages and caves in southern Kandahar province, Shields said.

The operation began Thursday as an intensified search for Taliban, al-Qaida and loyalists of renegade rebel leader Gulbuddin Hekmatyar, whom U.S. authorities have branded a terrorist.

No exchanges of fire or coalition injuries have been reported in the operation, Army officials said.

Troops also apprehended two other suspected rebels and seized a much smaller cache of ammunition and light machine guns on Friday, Army spokesman Col. Roger King said earlier.

Shields said that smaller cache included documents that referred to regional leaders of rebel forces. He declined to give further details.

In the attack Saturday, gunmen opened fire on an Afghan army post in the southern province of Kandahar, killing three Afghan soldiers, a senior Afghan government official said.

The gunmen traded fire with soldiers in the Wath army post, about 20 miles south of Spinboldak, for about an hour, then fled, said Fazaluddin Agha, the head of administration in Spinboldak district, near the border with Pakistan. He said they were believed to be from the former Taliban regime or with the radical Muslim group Hizb-e-Islami.

Separately, Afghan soldiers on the U.S.-led sweep seized bombs, guns and ammunition and arrested 13 people said to be linked to the former Taliban regime, Abdul Raziq, police chief of Spinboldak district, where part of the search was conducted.

Authorities were questioning the men — five of whom admitted having links with the Taliban, he said.

"They have made confessions and we have got proof" of their connection to the Taliban, according to Raziq, adding papers in the men's possession proved the links. He would not provide any details.

"We have got information about other friends of these people and are looking to arrest them," Raziq added. He said U.S. forces and about 100 Afghan troops were patrolling the border areas with Pakistan in Spinboldak for Taliban remnants.

About 600 ground troops began Valiant Strike Thursday about 60 miles east of the city of Kandahar, King said. Romanian infantry also were taking part. Apache attack helicopters and up to 400 support personnel backed the ground forces.

"The whole idea is never to let the enemy rest long enough to reorganize, regroup, recruit or retrain," King said.