The Taliban on Monday declared a three-day ceasefire across Afghanistan to mark this week's Eid al-Fitr holiday, just two days after being blamed for killing more than 50 people -- mostly young girls -- in a bomb attack outside a school in the capital.

The interior ministry reported Monday that at least 11 people were separately killed just hours before the Taliban announcement by a bomb that struck a bus in restive Zabul province.

The ceasefire announcement comes as the United States continues to pull out its last 2,500 troops from the violence-wracked country despite faltering efforts between the Taliban and the Afghan government to end a decades-long war.

"Mujahideen of the Islamic Emirate are instructed to halt all offensive operations against the enemy countrywide from the first till the third day of Eid," a statement released by the Taliban said. "But if the enemy conducts any assault or attack against you during these days, stand ready to robustly protect and defend yourselves and your territory," it added.

Eid al-Fitr marks the end of the Muslim fasting month of Ramadan, and the holiday begins according to the sighting of the new moon. The Taliban declared similar ceasefires last year to mark Islamic holidays.

The government usually reciprocates with a truce, and Fraidon Khawzon -- spokesman for chief negotiator Abdullah Abdullah -- said early Monday: "We welcome the announcement....the Islamic republic is also ready and will announce soon."

'Bodies piled on top of each other'

The latest offer comes after the government blamed the Taliban for Saturday's attack outside a girls' school in Dasht-e-Barchi, a suburb of the capital largely populated by the Shiite Hazara community, which is often targeted by extremist Sunni Islamist militants.

A series of blasts outside the school -- when residents were shopping ahead of the holiday -- killed more than 50 people and wounded over 100. It was the deadliest attack in more than a year. The Taliban, who denied responsibility, had earlier issued a statement saying the nation needed to "safeguard and look after educational centres and institutions".

On Sunday, relatives buried the dead at a hilltop site known as "Martyrs Cemetery", where victims of attacks against the Hazara community are laid to rest. Hazaras are Shiite Muslims and considered heretics by extremist Sunnis. Sunni Muslims make up the majority of the Afghan population.

Bodies in wooden coffins were lowered into graves one by one by mourners still in a state of shock and fear, an AFP photographer said. "I rushed to the scene (after the blasts) and found myself in the middle of bodies, their hands and heads cut off and bones smashed," said Mohammad Taqi, a resident of Dasht-e-Barchi, whose two daughters were students at the school but escaped the attack. "All of them were girls. Their bodies piled on top of each other."

Books and school bags belonging to the victims still lay scattered at the site of the attack. Interior ministry spokesman Tareq Arian told reporters at least 28 people were wounded in Monday's Zabul bus blast. The Taliban insist they have not carried out attacks in Kabul since February last year, when they signed a deal with Washington that paved the way for peace talks and withdrawal of the remaining US troops. The Taliban have clashed daily with Afghan forces in the rugged countryside even as the US military reduces its presence.

Taliban chief warns US

The United States was supposed to have pulled all forces out by May 1 as agreed with the Taliban last year, but Washington pushed back the date to September 11 -- a move that angered the insurgents. The leader of the Taliban, Hibatullah Akhundzada, reiterated in a message released ahead of Eid that any delay in withdrawing the troops was a "violation" of that deal.

"If America again fails to live up to its commitments, then the world must bear witness and hold America accountable for all the consequences," Akhundzada warned in Sunday's message.

Afghan President Ashraf Ghani has declared a day of national mourning for Tuesday. "This savage group does not have the power to confront security forces on the battlefield, and instead targets with brutality and barbarism public facilities and the girls' school," he said in a statement.

Saturday's blasts drew widespread global condemnation. Pope Francis called it "an inhumane action", while Iran blamed the jihadist Islamic State. India, meanwhile, called for the dismantling of "terrorist sanctuaries" and a ceasefire to boost peace efforts.