A militant attack is taking place at the American University in the Afghan capital, Kabul.
A large explosion has been heard and frightened students barricaded inside rooms in the building say they can hear gunfire close by.
At least one person has died and at least 12 are injured, officials say.
Police have described the attack, which began at about 19:00 local time (14:30 GMT), as “complex” and have deployed special forces.
The university president, Mark English, told AP news agency that a militant attack was underway and “we are trying to assess the situation”.
An interior ministry official said he thought several gunmen, some with suicide vests, were involved.
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Student Ahmad Mukhtar told the BBC that he was 100m (320ft) away from the university’s main entrance when he heard “six or 10” shots and a “huge” blast.
The explosion created so much light that it momentarily lit up the surrounding area, he said.
Then there were was more firing inside the campus. He added that he had also heard students shouting.
“I climbed a six-metre wall to escape,” Ahmad said.
Another student told AFP news agency he was stuck inside his class with other students.
“I heard explosions, and gunfire is going on close by,” he said by telephone. Other trapped students were tweeting or posting on Facebook desperate pleas for help.
Among them was Massoud Hossaini, a Pulitzer prizewinning photojournalist – though he was later reported to have escaped.
The attack comes two weeks after two university staff – one American, one Australian – were kidnapped by unknown gunmen. Their whereabouts remain unknown.
The university, which first opened its doors to students in 2005, is a non-profit private university chartered in the US.
It offers English courses, adult professional qualifications and bachelor degree programmes, among others.
About 1,700 students are enrolled; many are adults who study part-time and also have jobs.
Kabul attack: Gunmen target American University}