American Black Hawk helicopters and at least eight U.S. armoured vehicles rushed to support dozens of Afghan troops battling the assailants at the three—building police complex in restive Kandahar province. It was unclear how many insurgents were involved in the attack.

Insurgent suicide bombers and gunmen stormed an Afghan police compound on Thursday, setting off explosions and firing assault rifles in a coordinated attack that killed six members of the Afghan security forces.

American Black Hawk helicopters and at least eight U.S. armoured vehicles rushed to support dozens of Afghan troops battling the assailants at the three—building police complex in restive Kandahar province. It was unclear how many insurgents were involved in the attack.

Fighting in Afghanistan has intensified recently, with insurgents coming from neighboring Pakistan as the annual spring fighting season gets under way.

Thursday’s attack began when four suicide bombers stormed police complex, said Zulmi Ayubi, a spokesman for the provincial governor. Three of the bombers blew themselves up, Mr. Ayubi said, while the fourth man exchanged fire with Afghan troops.

“I heard a blast and after that continuous fighting with rocket launchers,” said Kandahar provincial policeman Ashrafullah Agha. After a third large explosion, Mr. Agha cut off the interview.

Four intelligence officers were killed in the fighting, along with an Afghan soldier and a police officer, said provincial police chief Khan Mohammad Mujahid. He said 12 police were wounded.

The police complex sits near the main highway between Kandahar and the capital of Kabul, 148 miles to the north. A weapons training school and police literacy center are located inside the complex. Kandahar is a Taliban stronghold that has seen some of the most intense fighting of the war.

Also on Thursday, NATO announced that it had concluded what it described as a “significant operation” in mountainous eastern Kunar province near the border with Pakistan.

More than 80 insurgents were killed after joint Afghan and coalition forces cleared militants out of four villages, NATO said.

“The combined security force moved into the mountainous area near the Pakistan border in order to disrupt insurgent activities in the region,” NATO said in a statement. “Insurgents had been using the area to move supplies and men into Kunar province and to stage attacks on Afghan and coalition forces.”

Afghanistan’s Ministry of Defence said late Wednesday that more than 130 insurgents were killed in the area over the past two weeks. Few details have been released, but at least six U.S. soldiers were killed in the area last week.

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