videos and photos can be seenhere
Media captionThe BBC’s Shahzeb Jillani said the attackers were heavily armed
Security forces have ended a gun and bomb attack on a university in north-west Pakistan in which 19 people were killed and 50 injured.
Four suspected attackers also died in a battle that lasted nearly three hours at Bacha Khan University in Charsadda.
There are conflicting reports about whether Pakistan Taliban militants carried out the assault.
The group killed 130 students at a school in the city of Peshawar, 50km (30 miles) from Charsadda, in 2014.
About 3,000 students are enrolled at Bacha Khan but hundreds of visitors were also expected on Wednesday for a poetry event.
Attack as it happened
Who are the Taliban?
Prime Minister Nawaz Sharif said in a statement, quoted by Reuters news agency: "We are determined and resolved in our commitment to wipe out the menace of terrorism from our homeland."
It could have been much worse - M Ilyas Khan, BBC News, Islamabad
There have been conflicting claims about who could be involved in the attack, especially given a kaleidoscopic mix of militant networks that is evolving along the Pakistan-Afghan border region in the north.
The attack comes amid a sudden spike in militant violence in Pakistan, after a year of relative peace and quiet largely attributed to a 2014 military operation against militant sanctuaries in Waziristan. Questions are now being raised over whether that operation really destroyed the ability of militants to regroup and strike at will.
The attack is reminiscent of the December 2014 attack on a school in Peshawar in which more than 150 people, mostly schoolboys, were killed. But damage to life and property this time has been much less, mainly due to swift action by the local police, but also because of the fact that the university had its own team of more than 50 trained security guards on duty who first confronted the attackers.
A dense fog that reduced visibility to less than 10m may also have been a factor, as one police officer explained, because it put the attackers at a disadvantage against the university guards who knew the premises better.
"The operation is over and the university has been cleared," Pakistani army spokesman Gen Asim Bajwa told Reuters news agency. "Four gunmen have been killed."
The attackers struck at around 09:30 local time (04:30 GMT), apparently climbing over a back wall under cover of the thick winter fog.
Intense gunfire and explosions were heard as security guards fought the attackers.
"I personally heard two explosions," an unidentified eyewitness told Pakistan’s Geo TV.
"We don’t know if they were suicide bombers or grenades. I personally saw two explosions and smoke was rising."
Students and staff ran to find cover in toilets and examination halls.
Geology student Zahoor Ahmed said his chemistry lecturer had warned him not to leave the building after the first shots were fired.
Media captionStudent Aizaz Khan says the security forces showed "great bravery"
"He was holding a pistol in his hand," he was quoted by AFP news agency as saying.
"Then I saw a bullet hit him. I saw two militants were firing. I ran inside and then managed to flee by jumping over the back wall."
Another student told television reporters he was in class when he heard gunshots.
"We saw three terrorists shouting, ’Allah is great!’ and rushing towards the stairs of our department," he said.
"One student jumped out of the classroom through the window. We never saw him get up."
Images from inside the university show a pool of blood on the floor of a dormitory and the charred corpses of two alleged militants lying on a staircase.
Grieving relatives gathered at a hospital as the bodies of victims were placed in coffins.
A senior Taliban commander, Umar Mansoor, told media that the attack was in response to a military offensive against militant strongholds. He said four suicide attackers had carried out the attack.
However, the group’s main spokesman, Mohammad Khurasani, later told the BBC the Taliban had not been involved. He condemned the attack as "un-Islamic".
An assistant professor at the university, Dr Shakoor, told the BBC he had turned back from the main gate of the campus after being told it was under attack.
Most of the students and members of the faculty would probably still not have arrived when the attack started, he said.
He saw people coming out through the main gate, apparently because the attackers had entered the campus from the back.
The university is located in an open area some distance east of Charsadda town, surrounded by open agricultural fields, and is therefore a soft target, the BBC’s Ilyas Khan reports.
Bacha Khan is a new university, founded in 2012, its website says.
Just days ago, some schools in Peshawar were closed by the authorities amid reports that militants were planning an attack.