At least 60 people have been killed and more than 100 injured in a car bomb attack at a hospital in Afghanistan's Logar province, local officials say.
The hospital building was destroyed and people buried under rubble. Casualties included women, children and elderly.
The Afghan health ministry said the attack was unprecedented and inhumane.
Officials blamed the Taliban, but a Taliban spokesman said the movement did not target civilians and the blast was caused by "someone with an agenda".
However, the BBC's Bilal Sarwary in Kabul says the Taliban is always careful to distance itself from major attacks with large numbers of civilian casualties.
An intelligence official later said the vehicle had been detonated close to the hospital after police had tried to stop it, and that it was not clear what the actual target was.
Provincial official Din Mohammad Darwaish said the death toll could well increase as there were still people buried.
Soldiers have been dispatched to the scene to try to pull out those that are trapped.
The attack follows a UN report earlier this month indicating a recent rise in civilian casualties.
It said May was the deadliest month for civilians in Afghanistan since records began in 2007, with 368 killed.
It added that 2,777 civilians died in 2010, making it the worst year, with three-quarters of the deaths blamed on insurgents.
'Disgust and hatred'
A large number of people had been gathering at the clinic, in Azra district, for weekly treatment, many of them women, children and elderly people, Mr Darwaish said.
"The target of the blast is not clear but what is obvious is that a hospital was attacked and civilians were killed," he said.
A statement by the public health ministry, quoted by AFP news agency, expressed "disgust and hatred" towards the perpetrators of the attack.
"This inhumane act is unprecedented in the history of the conflict in our country and targeted a place where wounds are healed and patients receive treatment," it said.
Doctors and nurses were also said to be among the dead.
A member of the Logar provincial council told the BBC: ''It is one of the saddest days. I have lost young, old, women, men - it is no less than a doomsday.
"The government and its intelligence agencies should have been able to prevent this. To the enemies of the people and Islam, I say, what do you get from a bloodbath like this? Almost every house, every family is grieving."
Our correspondent says there has never been an attack on a hospital in Afghanistan on this scale, although last month a suicide bomber attacked the main military hospital in Kabul, killing six people.
There is almost no central government control over Azra, which is close to the Pakistan border, and insurgents and smugglers are well-established there, he adds.
On Friday 10 people were killed and 24 injured in a blast in the northern Kunduz province.
Two days earlier, US President Barack Obama announced a partial troop pullout from Afghanistan.
He said 33,000 troops would leave this year, with the remaining 68,000 departing by 2013.
But there are concerns among the top US military that the withdrawal will be more risky than they have advised.
The problem is the Taliban belong to the land, but on the other hand, the Al-Qaeda fighters are not. It is not in the interest of the Taliban to antagonize the people, though they have from time to time.
STGOD: Byzantine Empire Your spirit, diseased as it is, refuses to allow you to give up, no matter what threats you face... and whatever wreckage you leave behind you.
Kreia
The Taliban hasn't relied on foreign volunteers for years, well if one discounts Pakistanis, so it seems unlikely this was an Al Qaeda operation. It is much more likely to have been some Pashtun or other tribal suicide bomber recruited from just across the border in the Tribal Frontier Areas, where the Taliban has free rein in Pakistan. It may be that the bomber detonated early after being detected by police, but the Taliban has carried out high casualty attacks on civilian targets before and disavowed them afterward. There really is nothing in the Taliban's previous behavior to suggest even remotely that this a fluke, though.
The unfortunate fact is that insurgent movements have every incentive in the world to carry out atrocities, and no real incentive not to. It is farcical to imagine them being brought to legal responsibility for them, and it almost never has any impact on the willingness of outsiders to support their cause. Atrocities are relatively cheap to commit, since civilians are much easier targets than soldiers, and often have much more media impact than any ambush could. Most of the time the rising death toll will be blamed on the government or occupation, which puts further political pressure on the stronger party to end the war as soon as possible in whatever way they can (IE, to withdraw or give in to the insurgency's political demands). They can help break internal opposition to the insurgency by intimidating or simply outright eliminating moderate elements and destabilize the state order that can protect the population at large. They can turn the population against the insurgency but that only matters if the state is able, through its own resources or outside support, to consolidate the security situation. And every atrocity is a blow against that consolidation.
So they aren't enough to win, but almost every modern insurgency has indulged in them as part of a strategy for victory. The Taliban is no different in that respect, and the Afghani government is venal, weak, and incompetent compared even to the Iraqi government. So the strategy has a significant chance of working just fine.
There is the moral of all human tales;
Tis but the same rehearsal of the past,
First Freedom, and then Glory — when that fails,
Wealth, vice, corruption, — barbarism at last.
-Lord Byron, from 'Childe Harold's Pilgrimage'
