KABUL (Reuters) - Afghan officials and villagers said 18 people, including women and children, were killed in a NATO air strike in the southeast on Wednesday, threatening to raise tensions with the Western military as it prepares to hand over control to local forces.
Another 20 civilians were killed when a pair of suicide bombers struck within minutes of each other outside the sprawling NATO base in the southern city of Kandahar.
It was the bloodiest attack in weeks since the Taliban launched a spring offensive.
Separately, NATO said a helicopter crashed in eastern Afghanistan killing two soldiers. It said the cause of the crash was being investigated but the governor of the southeastern province of Ghazni, Musa Akbarzada, said Taliban insurgents shot down a helicopter. The insurgents also said they had downed the chopper.
Violence has surged across Afghanistan this summer with the Taliban vowing to target the Afghan government and security forces, as well as the 130,000 foreign troops in the country, most of whom are due to leave by the end of 2014.
Tahir Khan Sabri, the governor of Logar province, which lies south of Kabul, said 18 villagers, most of them women and children gathered for a wedding, were killed in an air strike conducted by NATO forces early on Wednesday.
"They were all civilians," he said, adding that President Hamid Karzai had ordered an investigation into the deaths.
The NATO-led International Security Assistance Force said it was looking very seriously at the reports of civilian casualties from the operation in Baraki Barak district to capture a senior Taliban commander.
The coalition earlier confirmed it had carried out an air strike in the district, but said initial operational reports only indicated that two women had suffered non-life threatening injuries and were treated at a military facility.
It said that a number of insurgents were killed in the operation conducted with Afghan forces.
But angry villagers said no Taliban were in the two houses that were destroyed in the air strike.
"In these houses nobody has been left alive. All are martyred whether they were male, female or children. They were not Taliban, they haven't fought with anyone, they haven't attacked anyone," Sayed Ahmad said.
A video taken by a local photographer showed gruesome images of bodies of children and women alleged to have been killed in the attack in the back of a van. Villagers said the families were preparing for a wedding two days later.
"If the government cannot step the Americans from killing civilians, it should order them out of the country," said Habibulrhman, another villager.
President Karzai repeatedly has warned against civilian casualties in military operations. He said last month that a strategic partnership agreement signed with the United States was at risk of becoming "meaningless" if Afghans did not feel safe.
Underlining the challenge facing security forces, two suicide bombers detonated their explosives in a parking area outside the sprawling NATO base in Kandahar which has been repeatedly attacked.
Four provincial governors from the south were at a meeting at the base when the attacks took place, General Abdul Hameed, Afghan army commander for the southern region, told Reuters.
A bomber on a motorcycle blew himself up in an area near the base packed with truck drivers and other civilians waiting to get into the facility.
A few minutes later, as people gathered at the site of the blast, another bomber on foot walked into the crowd and detonated his explosives, said Ahmad Faisal, a spokesman for the provincial governor.
Kandahar, the birthplace of the Taliban, has seen some of the worst attacks.
The violence has stoked concern that Afghan forces may struggle against a Taliban insurgency at its deadliest once most Western combat troops leave by the end of 2014.
Reporting by Ismail Sameem; Writing by Sanjeev Miglani; Editing by Michael Roddy