The Pakistani city of Peshawar is burying its dead after a Taliban attack at a school killed at least 132 children and nine staff.
New images from the school show the brutality of the attack, with pools of blood on the ground and walls covered in pockmarks from hundreds of bullets.
Mass funerals and prayer vigils for the victims are currently under way.
Gunmen had walked from class to class shooting students in the Pakistani Taliban's deadliest attack to date.
Prime Minister Nawaz Sharif declared three days of mourning over the massacre, which has sparked national outrage.
He also announced an end to the moratorium on the death penalty for terrorism cases, which correspondents say is a move aimed at countering a view held by many Pakistanis that many terror suspects end up evading justice.
World leaders have also voiced disgust at the attack, which even the Afghan Taliban have criticised.
Separately, Pakistan's army says it launched air strikes at militants in the Khyber and North Waziristan areas, although it is not yet clear if this was a direct response to the school attack. An offensive against the militants has been going on since June.
At the scene: Mishal Husain, BBC News
It is a very eerie atmosphere. These are premises that should be alive at a time of day like this to the sound of hundreds of children who studied here and began school as normal on Tuesday. But it is desolate now.
The army has been working through the night to clear the premises of explosives.
I am standing now at the bottom of the white stone steps that lead up to the auditorium. There are blood stains running right down the steps and towards the auditorium itself.
There is a child's shoe on one of the steps. The auditorium, where children were taking exams, was one of the places within the school grounds that the militants first targeted.
As I peer in now, the chairs that the children were sitting on are upturned, the place has been turned upside down and again I can see the blood stains on the floor right around me.
Mr Sharif also convened a meeting of all parliamentary parties in Peshawar to discuss the response.
Meanwhile, Pakistan's army chief General Raheel Sharif is in the Afghan capital, Kabul, on a surprise visit to discuss security co-operation aimed at tackling the Taliban insurgency.
Pakistani Taliban (TTP) leader Mullah Fazlullah is believed by the Pakistani authorities to be hiding in Afghanistan and media reports in Pakistan suggest the school attack may have been co-ordinated from Afghanistan.
But the TTP said the attack had been masterminded by its military chief in the Peshawar region, who it said had been in touch with the gunmen throughout the assault.
A TTP spokesman told the BBC they had deliberately killed older pupils and not targeted "small children".
BBC correspondents say the Taliban statement is being seen as damage limitation after the attack was universally condemned in Pakistan for its brutality.
The TTP also repeated its earlier claim that only six attackers were sent, contradicting official accounts that seven gunmen were killed. The militants say the attack was revenge for the army's campaign against them, and that they chose the school as a target because their families had also suffered heavy losses.
Scenes of devastation
Reporters visiting the school for the first time saw pools of blood marking the floor and torn notebooks, clothing and shoes among the debris.
"This is not a human act,'' military spokesman Major General Asim Bajwa said during a tour of the school, the Associated Press reports. "This is a national tragedy."
Seven Taliban attackers wearing bomb vests cut through a wire fence to gain entry to the school, before launching an attack on an auditorium where children were taking an exam.
Gunmen then went from room to room at the military-run school, shooting pupils and teachers where they found them in a siege that lasted eight hours, survivors say.
A total of 125 people were wounded at Peshawar's Army Public School, which teaches boys and girls from both military and civilian backgrounds. All seven attackers were killed, while hundreds of people were evacuated.
Mohammad Hilal, a student in the 10th grade, was shot three times in his arm and legs when the gunmen stormed the school auditorium.
"I think I passed out for a while. I thought I was dreaming. I wanted to move but felt paralysed. Then I came to and realised that actually two other boys had fallen on me. Both of them were dead," he told the BBC.
Zulfiqar Ahmad, 45, the head of the mathematics department who was shot four times during the attack told the BBC he did not believe any of the 18 students in his class had survived.
The victims are also being mourned elsewhere, with India's parliament observing a minute's silence in their honour.
India's Prime Minister Narendra Modi offered his country's "deepest condolences".
Mr Sharif pledged to avenge a "national tragedy unleashed by savages".
Malala Yousafzai, the 17-year-old who was shot by the Pakistani Taliban for championing girls' rights to education, also condemned "these atrocious and cowardly acts".
Pakistani embassies worldwide have lowered their flags to half-mast and opened books of condolences.
Deadly attacks in Pakistan
16 December 2014: Taliban attack on school in Peshawar leaves at least 141 people dead, 132 of them children
22 September 2013: Militants linked to the Taliban kill at least 80 people at a church in Peshawar, in one of the worst attacks on Christians
10 January 2013: Militant bombers target the Hazara Shia Muslim minority in the city of Quetta, killing 120 at a snooker hall and on a street
28 May 2010: Gunmen attack two mosques of the minority Ahmadi Islamic sect in Lahore, killing more than 80 people
18 October 2007: Twin bomb attack at a rally for Benazir Bhutto in Karachi leaves at least 130 dead. Unclear if Taliban behind attack
In Afghanistan itself, the local Taliban described the school attack as un-Islamic and said they were sending condolences to the families of the victims.
The Afghan Taliban are currently stepping up their own attacks in Afghanistan and share roots with the Pakistani Taliban and usually share the same ideology too, the BBC's Mike Wooldridge reports from Kabul.
Hundreds of Taliban fighters are thought to have died in the recent Pakistan army offensive in the Khyber area and North Waziristan, regions close to the Afghan border.