Afghan and Canadian forces moved into villages outside Kandahar on Wednesday to root out Taliban militants, killing at least 36 insurgents, while an explosion elsewhere killed four British soldiers, officials said.

Troops in Arghandab district just outside of Kandahar, southern Afghanistan's largest city, exchanged fire with militants during "a few minor contacts," NATO spokesman Mark Laity said.

The Afghan Defense Ministry said more than 20 Taliban fighters had been killed in Tabin, a village in Arghandab, while 16 fighters were killed in Khohak, also in Arghandab. Two Afghan soldiers also were killed, the ministry said in a statement. The 12 other militants killed were in nearby Maiwand district, the ministry said.

A top provincial official in Kandahar, Ahmed Wali Karzai, the brother of Afghan President Hamid Karzai, said hundreds of families had fled to the city, and that some of the villages had already been cleared of Taliban.

Helicopters and jets patrolled the skies and smoke rose from fields after exchanges of fire, an Associated Press reporter at the scene said. A helicopter landed in a field near the fighting and appeared to evacuate a casualty, he said. Large Canadian military vehicles and Afghan police trucks were moving through the region.

Afghanistan's Ministry of Defense on Tuesday said between 300 and 400 militant fighters were operating in Arghandab — a lush region of pomegranate and grape fields that lies 10 miles northwest of Kandahar city, the Taliban's spiritual home.

Canadian military officials who patrolled through Arghandab over the last day reported "no obvious signs" of insurgent activity. But that didn't mean there were no Taliban there, a NATO news release said. Pentagon officials said reports of hundreds of Taliban in Arghandab were being overstated.

However, Karzai, the director of the provincial council, said more than 1,500 families had sought refuge in Kandahar out of fear, many staying with relatives. He said at least 100 Afghan troops were engaged in the fighting.

Meanwhile, the British Ministry of Defense said four British soldiers were killed when an explosive was detonated against their vehicle during a patrol in neighboring Helmand province on Tuesday. At least one soldier was wounded.

It was one of the deadliest attacks of the year on international troops. Four U.S. Marines were killed in a roadside bomb in nearby Farah province earlier this month, but prior to that, no more than three international troops had been killed in any one attack in Afghanistan this year.

The Taliban have long sought to control Arghandab and the good fighting positions its pomegranate and grape groves offer. With control cemented, militants could cross the countryside's flat plains for probing attacks into Kandahar, in possible preparation for an assault on their former spiritual home.

Haji Agha Lalai, a provincial council member and the head of the province's reconciliation commission, which brings former insurgents who lay down their weapons back into the folds of society, said the militants had been destroying bridges and planting mines as defensive measures in hopes they can repel attacks from Afghan and NATO forces.

"From a strategic military point of view, Arghandab is a very good place for the Taliban," Lalai said. "Arghandab is close to Kandahar city, allowing the Taliban to launch ambushes and attacks more easily than any other place in the province. Secondly, it's covered with trees and gardens — they can easily hide from air strikes."

The Taliban assault on the outskirts of Kandahar was the latest display of strength by the militants despite a record number of U.S. and NATO troops in the country. The push into Arghandab came three days after a coordinated Taliban attack on Kandahar's prison that freed 400 insurgent fighters.

The hardline Taliban regime ousted from power in a 2001 U.S.-led invasion of Afghanistan regarded Kandahar as its main stronghold, and its insurgent supporters are most active in the volatile south of the country.