Kabul, Afghanistan: Explosions and gunfire rocked the American University of Afghanistan in Kabul on Wednesday, an official and students trapped inside classrooms told AFP, in the latest militant attack in the Afghan capital.

‘I heard explosions and gunfire is going on close by... our class is filled with smoke and dust,’ a desperate student told AFP by telephone.

‘We are stuck inside and very afraid.’

Many other trapped students were tweeting desperate messages for help. Among them was Associated Press photojournalist Massoud Hossaini. 

No militant group has so far claimed responsibility for the attack, which comes as the Taliban step up their summer fighting season against the Western-backed Kabul government.

‘#AUAF under attack. I along with my friends escaped and several other of my friends and professors trapped inside,’ Kabul-based journalist Ahmad Mukhtar tweeted.

The Italian-run Emergency Hospital in Kabul tweeted that at least five wounded people had been brought to the facility for treatment. 

The management of the elite American University of Afghanistan, which opened in 2006 and enrols more than 1,700 students, was not immediately reachable for comment.

The private university is usually packed with students in the evening, many of them working professionals doing part-time courses at the facility. 

The assault comes after two professors at the university -- an American and Australian -- were kidnapped in the heart of Kabul earlier this month, the latest in a series of abductions of foreigners in the conflict-torn country.

No group has publicly claimed the abductions so far. The Afghan capital is infested with organised criminal gangs who stage kidnappings for ransom, often targeting foreigners and wealthy Afghans, and sometimes handing them over to insurgent groups.

It appeared to be the first reported abduction related to a private university in Afghanistan.

The Taliban have stepped up nationwide attacks.

Afghan forces backed by US troops are seeking to head off a potential Taliban takeover of Lashkar Gah, the capital of the southern opium-rich province of Helmand as fighting intensifies.

A roadside bomb killed an American soldier on Tuesday near the city, and left another American and six Afghan soldiers wounded, the US-led NATO coalition said.

The turmoil convulsing Helmand, blighted by a huge opium harvest that helps fund the insurgency, underscores a rapidly unravelling security situation in Afghanistan.

Fighting has left thousands of people displaced in Helmand in recent weeks, sparking a humanitarian crisis as officials report food and water shortages.

The Taliban have also closed in on Kunduz -- the northern city they briefly seized last year in their biggest military victory so far -- leaving Afghan forces stretched on multiple fronts.

But coalition forces have insisted that neither Kunduz nor Lashkar Gah are at risk of falling to the insurgents.