On a day of deadly violence that underlined the vulnerability of Afghans, , more than 30 civilians were killed by Taliban suicide attackers and a Nato air strike on Wednesday.

Civilians are regular victims of the fighting that now affects most of Afghanistan, and last year a record number of innocent people were killed, according to UN data, but it is unusual for both parties in the conflict to exact such a toll within the span of a few hours.

In the southern city of Kandahar, a bomber struck in a market near the gates of a large military airbase. As crowds gathered at the site of the attack, a second man drove up on a motorbike and detonated another suicide vest. Together they killed 21 civilians and injured at least 50, the provincial police chief, Abdul Razzaq, said.

In Logar province, which lies south of Kabul but near the eastern border with Pakistan, a Nato air attack on a village home killed up to 18 civilians who had gathered to celebrate a wedding, local government and security officials said.

The attack targeted Taliban fighters who had taken shelter in the house, but among the bodies that angry villagers brought to the provincial capital were at least five women and seven children, according to a photographer from the Associated Press who saw the dead.

It is not clear whether the insurgents sought permission to enter the house, or forced their way in at gunpoint. There were also at least half a dozen militants among those killed, the police and intelligence services said, but villagers were only mourning their own dead.

"Last night in Baraki Barak district there was fighting between the Taliban and foreigners and the Taliban hid themselves in the house of a man called Basir Akhunzada, an elder of the people," said Abdul Wali, the chief of the Logar provincial council, who discussed the bombing by phone from Logar.

"Akhundzada was killed, his brother Qayoum Akhunzada, Qayoum's wife. Altogether 18 civilians from his family were killed."

An official from the provincial governor's office confirmed that 18 civilians died. "Not all the people were from his immediate family, because there was a wedding ceremony going on, so there were many relatives staying there," said adviser Mirwais Mir Zakhwal.

Nato forces said they had requested an air strike in Baraki Barak after troops were attacked with guns and rocket-propelled grenades, but listed "multiple insurgents" as the only dead. A spokesman said the Nato-led coalition was looking into allegations of civilian casualties.

"We are still looking into the circumstances to try and understand what took place there, and the nature of the casualties," said Lieutenant Commander Brian Badura.

The Taliban claimed responsibility for the attack in Kandahar but said it was aimed at the base, Nato's largest headquarters in the south, and claimed they killed only foreigners. But the bombers targeted an area with a bazaar and bus station where there are few foreigners. Afghan security and health officials said the dead and injured were all Afghans.

"I was sitting in my shop, close to this gate, and heard a small explosion, then I saw people were left killed and wounded on the ground," said Shamsullah, a young shopkeeper injured in the blast. "After a few minutes a motorbike came and I just heard a very big explosion and when I opened my eyes I was in a hospital."

The use of a second bomb to increase the toll – by targeting security forces, medical services and bystanders gathered around victims of a first blast – is unusual in Afghanistan. A spokesman for the Kandahar provincial governor, Jawed Faisal, said he could remember only two other attacks in the city, which is a regular insurgent target, that used secondary bombs. One was in 2007 and one in 2010.

The attack, which happened as four provincial governors were meeting at the base, was condemned by Afghanistan's president, Hamid Karzai, the US embassy and by the Nato-led coalition.

Karzai has long criticised Nato for not doing enough to prevent the killings of innocent civilians, which have become a major irritant in relations with his foreign partners.

He warned earlier this month that the deaths could undermine a deal laying the framework for ties with the US after 2014, when most foreign combat forces will have left Afghanistan.

His critics in turn say the Afghan president should be stronger in his condemnation of the Taliban's role in pushing up the country's civilian casualty toll. Insurgents are now responsible for more than three-quarters of these deaths, according to UN figures.

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