A homicide bomber attacked a police drug eradication unit in southern Afghanistan on Thursday, killing five people and wounding 17 others, an official said. The Taliban claimed responsibility.

The attacker struck the patrol in Lashkar Gah, the capital of Helmand province, a major drug-producing area, said Kamal Uddin, the deputy provincial police chief.

The members of the force were traveling in a convoy of vehicles headed for nearby districts to eradicate poppies at the time of the blast, Uddin said.

Five people — two police officers and three civilians — were killed in the blast, said Daud Ahmadi, the spokesman for the provincial governor. The blast also wounded four policemen and 13 civilians, Ahmadi said.

Two police vehicles and three shops were damaged in the explosion, Uddin said. He initially reported four dead policemen, but the casualty figures were later revised by Ahmadi.

A spokesman for the Taliban claimed responsibility for the blast in a phone call to an Associated Press reporter in southern Afghanistan.

In a statement, the Interior Ministry blamed "the narcotics mafia" for the attack.

Afghanistan is the world's largest producer of opium, the main ingredient in heroin. The Afghan opium trade accounts for 90 percent of worldwide production. The U.N. estimated last year that up to $500 million from the illegal drug trade flows to Taliban fighters and criminal groups.

The top U.S. and NATO commander in Afghanistan, Gen. David McKiernan, said his troops have increased their targeting of drug operations by eight- or 10-fold in the past four months, specifically for drug lords or operations that could be tied to insurgents and insurgent funding.

McKiernan told newspaper executives gathered at The Associated Press annual meeting Monday that heroin trafficking was "a debilitating system across this country that eats away at good governance, eats away at progress and it certainly provides a funding source for the insurgency."

On Wednesday, a raid by U.S. coalition troops in eastern Khost province killed four people, including two women, and wounded another woman, the coalition said in a statement Thursday. The coalition at first labeled the four militants, but later said it appeared that was not the case.

"Coalition forces are working closely with local Afghan officials and family members to express condolences and provide assistance in the aftermath of this tragic event," a U.S. statement said.

The issue of civilian deaths at the hands of U.S. and other foreign troops has caused friction between President Hamid Karzai and his government's foreign backers in the country.

Karzai has demanded many times that raids by foreign troops on Afghan villages stop, and that any operation should be done in coordination with Afghan authorities.

U.S. and NATO officials say the militants regularly operate from civilian areas, thus putting civilians in danger.

Separately, six alleged militants were killed and another detained in a coalition operation in the southern province of Kandahar late Wednesday, the coalition said.

Southern Afghanistan is the center of the Taliban-led insurgency, where thousands more U.S. troops have been ordered to join the fight by President Barack Obama to try to reverse militant gains in the last three years.