In some of the deadliest combat since the Taliban's fall, hundreds of militants with machine guns stormed a town, battled Afghan, U.S. and Canadian forces and set off car bombs.

More than 100 people were killed, including dozens of insurgents and a U.S. civilian, officials said Thursday.

The violence, which has raised new fears for the future of Afghanistan's fragile democracy, was concentrated in the southern provinces of Helmand and Kandahar, the former heartland of the hardline Islamic regime ousted in a U.S.-led 2001 invasion for hosting Al Qaeda.

CountryWatch: Afghanistan

The Taliban have stepped up attacks in recent months, with roadside bombs and suicide assaults, but the fighting that raged Wednesday night and Thursday marked an escalation of the conflict in a region where the U.S.-led coalition is set to cede control of security operations to NATO by July.

The Taliban death toll from fighting ranged up to 87, U.S. and Afghan officials said.

Fifteen Afghan police officers and a Canadian officer were killed.

Capt. Nichola Goddard, who died in a clash in Kandahar, was Canada's first female soldier to die in combat.

Two homicide bombings elsewhere in Afghanistan claimed two lives, including an American civilian working on a U.S. project to train Afghan police.

Ron Zimmerman, 37, of Connersville, Indiana, died in an attack in the western city of Herat near the Iranian border, his family said. U.S. Embassy spokesman Chris Harris said two other Americans were wounded.

The blast incinerated the vehicle and left a severed limb laying in the road, witnesses said.

An Afghan driver was later killed at the site by gunfire from U.S. investigators and military personnel who feared another suicide attack when the driver ran through a checkpoint, the U.S. Embassy said.

Afghan President Hamid Karzai on Thursday said the violence was emanating from neighboring Pakistan, whose mountainous border tribal regions are also populated by ethnic Pashtuns, who make up the majority of the Taliban militants.

"We have credible reports that inside Pakistan, in the madrassas, the mullahs and teachers are saying to their students: 'Go to Afghanistan for jihad. Burn the schools and [medical] clinics,"' Karzai said.

Pakistan's Foreign Ministry spokeswoman, Tasnim Aslam, called the allegations "baseless."

In one of the largest militant attacks since 2001, an estimated 300-400 militants using assault rifles and machine guns attacked a police and government headquarters late Wednesday in the small town of Musa Qala in Helmand, sparking eight hours of clashes with Afghan security forces.

The bodies of about 40 Taliban militants were recovered, said deputy Gov. Amir Mohammed Akhunzaba. Thirteen police were killed and six wounded in the fight, some 280 miles southwest of Kabul.

The fighting was the fiercest in Helmand province since the fall of the Taliban, Akhunzaba said.

The assault was countered by Afghan police reinforcements, who eventually forced the militants to flee, said British military spokesman Capt. Drew Gibson.

British forces in Helmand province helped evacuate casualties but did not provide military backup, in part so Afghan police could prove their fighting abilities, Gibson said.

"If they're the ones who are seen beating off the Taliban, there's a lot of credibility for them," Gibson said. "The ANP [Afghan National Police] did admirably in the circumstances, proven by the fact that Musa Qala is now back under ANP security."

In neighboring Kandahar province, the U.S.-led coalition said up to 27 Taliban militants were killed during an operation Thursday. The military said there were seven confirmed deaths and another 15-20 militants may have been killed in an airstrike near the village of Azizi.

Elsewhere in Kandahar, about 18 Taliban militants and the Canadian officer, Goddard, were killed in fighting late Wednesday, said Maj. Scott Lundy, a Canadian military spokesman.

Canadian soldiers were supporting Afghan forces on a mission to oust Taliban fighters in Panjwayi district, about 20 miles west of Kandahar city, when they were attacked with rocket-propelled grenades and small-arms fire, Lundy said.

Three Afghan soldiers were wounded, and about 35 militants were detained, he said.

Although Canadian women lost their lives in action in both world wars, Goddard, from Calgary, Alberta, was the first to do so in a combat role.

A Defense Ministry spokesman, Gen. Zahir Azimi, said the impending handover of power in the south to NATO troops in July could be sparking attacks in the south of Afghanistan.

"Maybe the Taliban is trying to show NATO that they are active there, but coalition and NATO forces are both strong," he said.

Lundy said coalition commanders were still studying whether the attacks Wednesday and Thursday across the south had been coordinated.

The escalating violence comes as NATO prepares to deploy thousands of extra troops and take over control of security operations from the U.S.-led coalition, which has been hunting for Taliban and Al Qaeda militants in the south since late 2001. Troops from nations including Canada, Britain and the Netherlands will be stationed there.

Canada's parliament narrowly voted late Wednesday night to extend the nation's military mission in Afghanistan by two years until February 2009.

By the end of this year, NATO will also assume command in the volatile eastern region of Afghanistan, where U.S. forces will continue to operate but under the military alliance.

Yet the violence has not been restricted to the south and east, amid signs the militants are expanding their operations.

The attack that killed the American occurred in Herat, a western city which has been largely peaceful for the past four years.

A second suicide bomber detonated a car packed with explosives near the gates of an Afghan army base in the central province of Ghazni, 70 miles south of Kabul, Alam said.

The blast killed the bomber and a civilian passing on a motorbike and wounded a man walking in the area. No soldiers at the base were hurt, he said.

Also in Ghazni, rebels ambushed two police patrols, killing two officers and wounding five, including the provincial deputy police chief, Alam said.