(reuters) -- Details of the attack remained unclear after a group of armed men seized a building under construction in a heavily populated area of the city.

"The number of attackers, possible casualties and their target is not yet clear," said Najib Danish, spokesman for the Ministry of Interior.

The Afshar area of Kabul where the attack was under way is close to a training facility of the National Directorate of Security, the main Afghan intelligence agency, as well as a private university.

Another government official said the attack was near the intelligence agency training centre.

Isis claimed responsibility in a statement on its Amaq news agency, in which it said two of its fighters had attacked an intelligence agency centre in Kabul.

The group, which first appeared in Afghanistan in 2015, has claimed responsibility for a number of attacks in Kabul over the past several months.

But much remains unknown about how it operates and many observers are sceptical about its ability to mount complex attacks on its own.

(Photo: AFP)