KABUL, Sept. 27 (Xinhua) -- An explosion and subsequent gun firing rocked the northern side of Afghan capital of Kabul near the airport on Wednesday, witnesses said.

"One blast occurred at around 11:00 a.m. (0630GMT) at a gate in northern enclosure of Kabul international airport. The blast was followed by gun firing and grenade firings," Mohammad Wasim told Xinhua.

Military helicopters were hovering over the site and the airport's sirens were heard shortly after the incident, he said.

Meantime, the Afghan Interior Ministry spokesman, Najib Danish, said on Twitter that a rocket struck surrounding area of Hamid Karzai International Airport, causing no casualties.

No group has claimed responsibility yet.

The attack happened as NATO chief and U.S. defense secretary arrived here to pay a visit to the militancy-hit country.

On Sunday, three Afghan civilians were wounded after a bomb attack hit a NATO military convoy in western side of Kabul.