Afghan policemen stand guard at the site of an attack at American University of Afghanistan in Kabul, Afghanistan August 24, 2016. [Photo/Agencies]

KABUL - At least one student was killed and nearly 20 persons injured after a car bombing and ensuing gunshots rocked a private college in the Afghan capital of Kabul on Wednesday evening, sources said.

"The terrorists attacked American University of Afghanistan (AUAF), by a suicide car bombing followed by gunmen firing on security guards and students. The initial findings showed that one student was killed and 20 others injured by the attack which occurred at roughly 07:00 pm local time," a security source told Xinhua anonymously near the site.

"About three attackers were involved in the incident. One attacker destroyed the building's perimeter by a car bombing to open the way for the second squad of gunmen," the source said, adding the exchange of fire between Afghan Special Operation Forces and attackers lasted for nearly three hours.

The targeted building is located along the four-line Dar-ul-Aman road which leads to the parliament building. At least three female students were among the injured, resident Mohammad Salim told Xinhua.

"The blast caused panic among the people. Some 100 students were rescued by security forces. Several students were trapped inside safe-rooms at the building during the clashes. As we heard the AUAF was threatened by Taliban militants over the past couple of years. Two AUAF teachers were kidnapped a couple of weeks ago. They are still missing," Salim said.

The students mostly working in NGOs and government offices were arriving for evening classes before the attack took place, he said.

Afghan Chief Executive Abdullah Abdullah has condemned the attack.

"I condemn this coward attack on AUAF. Attacking schools, universities and innocent people is a war crime. We cannot bear it," he tweeted.

Further details about the incident are still forthcoming amid the absence of official statement.

No group has claimed responsibility for the attack yet.

About 1,600 civilians were killed and more than 3,560 others wounded in conflict-related violence and Taliban-led attacks in the first half of the year, according to UN mission officials in the country.