Black-clad Pakistani commandos overpowered a group of militants who had seized a police academy, taken cadets hostage and killed at least six of them Monday.

The killings represented a dramatic challenge to the government that faces U.S. pressure to defeat Islamic extremists.

The security forces stormed the compound on the outskirts of Lahore to end the eight-hour siege by the grenade-throwing gunmen, with three militants blowing themselves up and authorities arresting four, officials said.

At least three other unidentified bodies were recovered.

Pakistan's top civilian security official said militant groups were “destabilizing the country,” suggesting the plot may have originated with Pakistani Taliban leader Baitullah Mehsud.

Meanwhile, a Taliban member claiming to speak on behalf of a shadowy little-known group called the Fedayeen al-Islam said it was behind the attack.

Earlier this month, gunmen ambushed Sri Lanka's cricket team in Lahore, killing seven people and underscoring the militants' ability to wreak havoc far from Pakistan's northwestern regions where al-Qaida and the Taliban have proliferated.

Attack follows crackdown

Both Lahore attacks followed a crackdown on the Pakistani group Lashkar-e-Taiba, blamed for the November 2008 siege in Mumbai, India, that killed 164. There has been speculation that Monday's raid was revenge for the crackdown.

The primary victims of both attacks were Pakistan's undermanned and underequipped police, a militant strategy that appears designed to expose state institutions as weak.

Nonetheless, a massive police response was quickly mounted Monday, one that included army soldiers, armored vehicles and helicopters.

The siege ended after security forces cornered several militants on the top floor of a building in the compound, where the gunmen had held about 35 hostages.

Interior Ministry chief Rehman Malik suggested the culprit could have been Lashkar-e-Jhangvi, a Punjab-based, al-Qaida-linked Sunni extremist group implicated in several other attacks in the country.

Lashkar-e-Jhangvi is one of several militant groups that operate well beyond Pakistan's northwest. Some of them, including Lashkar-e-Taiba, have their roots in the Kashmir dispute with India, and Pakistani spy agencies are believed to have helped establish them.

Lashkar-e-Taiba has denied links to the Mumbai or cricket attacks.

‘Arms are coming in'

Malik also said the plot may have originated with the Pakistani Taliban in the northwest – noting that one of the arrested attackers was Afghan – and added that “some rival country,” a usual reference to India, was trying to derail democracy in Pakistan.

“In our country, at our different borders, arms are coming in, stinger missiles are coming in, rocket launchers are coming in, heavy equipment is coming – it should be stopped,” he told state TV. “Whoever the anti-state elements are, they are destabilizing the country.”

Last week, President Obama pledged more aid to Pakistan to help it fight militancy, while also urging it to tackle the “cancer” of extremism. He also warned that Pakistan could not expect a “blank check.”