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Rahmatullah Naikzad, Associated Press
Face covered former Taliban militants stand during a joining ceremony with the Afghan government in Ghazni, west of Kabul, Afghanistan, Monday, Jan. 16, 2012. About 25 former Taliban militants from Ghazni province handed over their weapons and joined with Afghan government as part of a peace-reconciliation program.

KABUL, Afghanistan — A suicide bomber on a motorcycle killed 12 Afghans, including two policemen, Wednesday in southern Afghanistan where three government officials have been assassinated so far this week, authorities said.

The suicide bomber blew himself at a bridge under construction in Kajaki district of Helmand province, according to Mohammad Ismail, the deputy of the Afghan security forces coordination office in the area. Ismail said NATO troops also were working at the construction site, but it was unclear whether any were injured or killed.

The coalition said it was aware of the incident but was still gathering information.

Daud Ahmadi, a provincial spokesman, says at least 23 others, including three policemen, were wounded in the blast.

Farther south in Helmand province, an Afghan intelligence official in Nad Ali district and two of this bodyguards were killed in an explosion, Ahmadi said. A remote-controlled bomb was detonated as the intelligence official, Wali Mohammad Khan, walked out of his house on Wednesday afternoon. A third bodyguard was wounded.

Taliban insurgents have assassinated hundreds of Afghan government officials and supporters in recent years, seeking to sap public confidence in President Hamid Karzai's administration.

On Tuesday in neighboring Kandahar province, a member of the Dand district council was assassinated while praying in a mosque in Kandahar city, and a member of the district council in Panjwayi was killed by gunmen on a motorbike.

Separately, NATO is investigating reports that five civilians, including one woman and two children, were accidentally killed during a night raid earlier this week in northeastern Afghanistan.

Sayed Fazelullah Wahidi, governor of Kunar province, said coalition helicopters fired into a compound Monday night in Chawkay district, killing two militants and the five civilians.

Coalition troops and Afghan special forces have been carrying out regular nighttime kill-and-capture raids against suspected insurgents across Afghanistan. But the operations and allegations of civilian deaths have provoked anger over foreign meddling in Afghanistan.

Karzai has demanded an end to the raids, saying that Afghan citizens cannot feel secure if they think armed soldiers might burst into their houses in the middle of the night.

Meanwhile, Afghan security forces said they had killed nine armed insurgents and captured 23 suspects in a series of raids in the past 24 hours.

An Interior Ministry statement issued Wednesday morning said the operations in eight different provinces also uncovered caches of weapons, ammunition and explosives.

The Afghan Defense Ministry says a soldier was killed and four were wounded in clashes with insurgents on Tuesday.

Associated Press Writer Mirwais Khan in Kandahar contributed to this report.