KABUL, Afghanistan >> A NATO airstrike targeting insurgents inadvertently hit two civilian homes in the volatile southwestern Helmand province, killing 12 children and two women, an Afghan government official said Sunday.

Dawood Ahmadi, a spokesman for the provincial government, said the alliance launched the airstrike late on Saturday in retaliation for an attack earlier in the day on a U.S. Marine base in Helmand’s northwest district of Nawzad. He said NATO hit two civilian houses, killing five girls, seven boys and two women.

NATO spokesman Maj. Tim James said a joint coalition and Afghan delegation was traveling Sunday to the site to investigate. He didn’t confirm the airstrike and provided no details about it or the attack on the Marines.

Civilian deaths are a constant source of tension between NATO and Afghan officials.

President Karzai blamed American troops for airstrikes that killed the 14 women and children and two men, injuring of six other civilians.

Afghan President Hamid Karzai has repeatedly called on coalition forces to minimize night raids and airstrikes and clear the operations with his forces.

"We have told the Americans and NATO forces several times that uncoordinated operations will result in the killing of innocent civilians and that such operations are inhumane, but still no one has listened," Karzai said Sunday, adding that his condemnation would be "the last warning to NATO forces, American forces, and American officials."

Helmand borders Pakistan and is an insurgent bastion. The province’s vast poppy fields are the Taliban’s prime profit center.

Afghan insurgents have stepped up a spring offensive across the country.

On Saturday, a Taliban suicide bomber wearing a police uniform blew himself up inside a heavily guarded compound in northern Afghanistan as top Afghan and international officials were leaving a meeting.

The blast killed two senior Afghan police commanders and wounded a German general in command of coalition troops in the region. Two German soldiers and two other Afghans were also killed in the blast that came just weeks before a planned drawdown of U.S. troops begins this summer.

The bomber detonated his explosives-laden vest inside the governor’s complex in Takhar province, where high-ranking Afghan officials were meeting with members of the international coalition.

Among the dead was Gen. Daud Daud, regional police commander in northern Afghanistan. Daud was a former deputy interior minister for counternarcotics and a former bodyguard of Ahmad Shah Massoud, the charismatic Tajik leader who commanded the Northern Alliance and died in an al-Qaida suicide bombing two days before the Sept. 11, 2001, attacks that provoked the U.S. invasion.

Also killed in the Saturday blast were provincial police chief Gen. Shah Jahan Noori, a secretary to the governor and one of Daud’s bodyguards, the health director said.

Gen. Markus Kneip, the NATO force’s commander for nine northern provinces, was among the wounded, German Defense Minister Thomas de Maiziere said in Berlin.

Abdul Jabar Taqwa, the Takhar province governor who was at the meeting and suffered burns to his head, hands and back, described the attack from a residence where he was recovering Sunday.

"General Kneip and I were about to leave the building," he said. "Suddenly, we heard a very big explosion. I didn’t know from which direction the sound came or what was going on … the explosion threw me out of the building and down the stairs."

Nine other Afghans were wounded, including a cameraman working in the governor’s office and eight Afghan troops.

The meeting focused on ways to prevent another violent protest in the northern province, where security has deteriorated as NATO and Afghan forces tackle insurgent strongholds in the south. Last week, 12 people died in Taloqan when a protest over a NATO raid that killed four deteriorated into a riot.

The Afghan public, which has grown increasingly hostile to foreigners as the nearly decade-long war continues, tends to perceive the NATO raids as capturing the wrong people or mistreating civilians during searches of private homes and compounds. The civilian casualties on Sunday were likely to add to the hostility.

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Khan reported from Kandahar, Afghanistan.