Militants armed with guns and rockets attacked the building of the Afghan Interior Ministry on Wednesday with casualties feared, sources and witnesses said.

"We heard a huge blast at the first gate of the ministry which is located near Charahi Shaheed Square. The blast occurred at midday. The whole place has now been sealed off," eyewitness Farhad Mohammadi told Xinhua.

"The initial information found that a suicide bomber detonated his explosive jacket in the front gate of the compound. Another group of the militants tried to breach the facility," a police officer who declined to be named told Xinhua.

"But the militants failed to reach the main building which is at the center of big open yard with high-profile security system."

"We still cannot provide details on causalities. There is fear of possible causalities," he added.

The number of the attackers also remained unknown and sporadic gunfire still could be heard as of 1:00 p.m. local time, he said.

The security forces have cordoned off the area for precautionary measures.

A four-line road which connects the Kabul airport with the city's Intercontinental Hotel passing the area was blocked for traffic after the attack.