NEW BAGHLAN, Afghanistan - President Hamid Karzai declared three days of mourning for victims of a suicide blast targeting a group of lawmakers and children, as the death toll on Wednesday rose to 60, making it the deadliest attack in Afghanistan since the 2001 U.S.-led invasion.

Hundreds of mourners gathered at a mosque near the site of the bombing in the town of New Baghlan, 150 kilometers north of Kabul, before moving to a simple hilltop graveyard to bury the dead.

"My son was supposed to finish school this year, but yesterday I had to peel off his blood-soaked clothes, and today I buried him,'' said an elderly man who broke down in tears at one grave site. He didn't give his name.

The numbers of the dead rose steadily throughout the day as officials collected information from village elders and families who buried their loved ones. It also emerged that lawmakers' bodyguards opened fire on the crowd after the bombing, wounding and possibly killing an unknown number of people.

Fifty-four people were buried in Baghlan province, said Mawlawi Sarajuddin, the head of the provincial council, while the bodies of six lawmakers were flown to Kabul.

Sarajuddin said most of the 54 were schoolchildren who had gathered to greet the visiting delegation. The Ministry of Education confirmed that at least 18 schoolchildren had been killed.

Karzai, joined by dozens of other Afghan leaders, watched honor guards carry the coffins of the six lawmakers from a helicopter and down a red carpet at Kabul's main airport Wednesday.

After the bombing Tuesday, shots were fired at the scene by lawmakers bodyguards, said Dr. Narmgui, a doctor at the New Baghlan hospital who witnessed the blast. Narmgui goes by one name.

Karzai ordered an investigation into the attack.

"There is no doubt this was a terrorist attack,'' Karzai told a news conference in Kabul.

He blamed the bombing on "the enemies of peace and security,'' a phrase often used for the militant Taliban, and directed authorities to conduct a thorough investigation. Such a spectacular attack also could have been the work of al Qaeda. The Taliban denied involvement.

The attack occurred as the lawmakers were being greeted by children on a visit to a sugar factory in Afghanistan's normally peaceful north.

Video obtained by AP Television News of the scene just before the blast shows schoolchildren, tribal elders and government officials lining the streets to greet 18 lawmakers as they were about to enter the factory.

Shafiqullah, 18, said he had not seen his younger brother since the attack and was looking for any signs that he was either alive or dead.

"My brother came here yesterday and after the incident he never returned home,'' Shafiqullah said. "I checked all the hospitals. I couldn't find him anywhere.''

Some of the children shook hands with the guests and one teenager handed red and pink roses to Sayed Mustafa Kazimi -- a former Afghan commerce minister and a powerful member of the opposition party National Front who was killed.

At least 42 of the 81 wounded were schoolchildren, said Mohammad Yousuf Fayez, a doctor at Baghlan's main hospital.

The video also shows an Afghan man holding the head of what he said was the suicide attacker, shouting "This is the guy who destroyed everything! This is the guy who killed us!''

No one claimed responsibility for the attack, and a purported Taliban spokesman, Zabiullah Mujahid, denied the militant group was involved.

"The Taliban doesn't target civilians,'' he said.

Taliban attacks typically target Afghan and international security forces or government leaders but often kill civilians nearby. Most of its attacks are in the country's south or east. Taliban bombers have killed regional governors in the past, but never so many public figures at once.

The northern region where the blast occurred is known for tensions between the mainly ethnic Tajik government leadership and remnants of the militant group Hezb-i-Islami, whose fugitive leader Gulbuddin Hekmatyar, an ethnic Pashtun, has joined the Taliban and al Qaeda in fighting the Afghan government, although he denies direct links.

In Washington, the White House called the attack "a despicable act of cowardice.''