At least 40 people have died in a suicide attack in northern Afghanistan, say hospital and provincial officials.
At least six members of the Afghan parliament, and reportedly many schoolchildren, were killed in the blast in the province of Baghlan.
The streets were left littered with bodies and awash with blood in one of the worst attacks in recent times.
Violence has spread in Afghanistan, where thousands of troops are battling the Taleban and their allies.
"This heinous act of terrorism is against Islam and humanity," President Hamid Karzai said in a statement.
The bomb exploded at a sugar factory in a town in Baghlan province while a delegation of parliamentarians was visiting - at least six of whom died.
Among the MPs killed was Mustafa Kazimi, a prominent opposition figure and former minister in Mr Karzai's government.
Schoolchildren who had gathered to welcome the politicians were also killed.
"I saw bodies lying in the streets and some of the people were stealing the weapons of the dead soldiers," local resident Mohammad Rahim told Reuters news agency.
"Children are screaming for help. It's like a nightmare," said Mr Rahim, who said the blast had killed his two cousins, both schoolgirls.
Witnesses saw the bomber just before he struck in the centre of the crowd - holding a bomb in one hand, and with an explosives belt around his chest - said the provincial governor.
The deputy mayor of Baghlan province said that two disembodied legs were all that remained of the bomber following the attack. The bomber's identity is unknown.
The head of hospitals in Baghlan, Yousuf Faiz, told AFP news agency 40 dead and 120 wounded had been registered at four hospitals.
Meanwhile provincial security chief Abdurrahman Sayedkhail told Reuters he was aware of 50 dead, though bodies remained on the streets and some relatives had already taken bodies away.
Members of the Nato-led force in Afghanistan are reported to be helping evacuate the wounded.
The BBC's Alix Kroeger in Kabul says such apparently political attacks have been rare in Baghlan province. She says private militias are known to operate there, but they usually limit their activities to common crime, mainly robbery.
President Karzai condemned the "heinous" attack - one of the worst since the ousting of the Taleban in 2001 - "in the strongest possible terms", he said in a statement.
"It is the work of the enemies of peace and security in Afghanistan," he said.
A Taleban spokesman has condemned the attack, denying the Taleban are behind it.
However, suicide bombs in Afghanistan have until now been exclusively the work of the Taleban and al-Qaeda, our correspondent says.
In a separate development, about 60 Taleban on motorbikes and in pick-up trucks captured an important town in the central province of Day Kundi - the third district they have taken in a week, along with two in western Farah province.
But our correspondent says they may not hold their new possessions for long - as their typical pattern is to mount an offensive, capture a centre and then retreat when police and the army counter-attack.
Until now, most suicide attacks have taken place in the south and east of Afghanistan or, less frequently, in Kabul.
But the United Nations says the number of suicide attacks is rising sharply, and insurgent violence has also been on the increase in areas of central and even northern Afghanistan which were previously relatively peaceful.
Civilians have often been the victims of the violence in Afghanistan - not only in attacks by insurgents, but also in strikes by the foreign Nato and US forces in the country.
The Taleban have not traditionally been active in Baghlan province, although they are known to be broadening their attacks across the country, says the BBC analyst Pam O'Toole.
Fighters loyal to Gulbuddin Hekmatyar, a former mujahideen leader who is fighting the Kabul government independently from the Taleban, are known to be active in Baghlan, she says.