KABUL (REUTERS) - Explosions and bursts of gunfire were heard near Kabul International Airport in the Afghan capital just after dawn on Thursday and black smoke rose above the facility, which is used by civilians and the military, a Reuters witness said.

The attack on the airport comes at a time of great uncertainty for Afghanistan as votes from the second round of a disputed presidential election are to be recounted. The poll is meant to mark Afghanistan's first democratic transfer of power.

A police source said a number of militants had burst into a building just north of the airport and opened fire. "Afghan security forces are dealing with it. More information will be released as soon as we get it," said the source, who asked not to be identified.

NATO forces said they were aware of reports of an attack on the airport but could not give more details.

A Reuters witness near the scene said he could see black smoke billowing above the airport and heard several explosions from what sounded like rocket-propelled grenades. A car had been set on fire not far from the scene.

Sediq Sediqqi, a spokesman for the Interior Ministry, said a rapid response force had been sent to the area.

On Tuesday, a car bomb detonated in a crowded market killed 43 people and wounded at least 74 in the eastern province of Paktika, close to Afghanistan's porous border with Pakistan.