An unknown number of U.N. employees were inside the building when it was attacked, said Dan McNorton, a spokesman for the United Nations Assistance Mission in Afghanistan. He had no information about any casualties.

The suicide car bomber destroyed the gate and at least three other militants — all wearing explosives vests — went inside, said Nabiq Arleen, a spokesman for the provincial governor of Herat province.

Afghan security forces exchanged gunfire with the attackers, killing at least one of them, said Ministry of Interior spokesman Zemeri Bashary.

NATO troops joined Afghan forces in surrounding the site. Helicopters flew overhead.

In the south, a photographer for The New York Times was seriously injured by a mine Saturday in Kandahar province where international forces are pushing into Taliban strongholds to try to turn the tide of the war.

No U.S. troops were wounded in the morning explosion.

A group of minesweepers and bomb-sniffing dogs had just moved over the area and were several steps ahead of Silva when the bomb went off.

Homemade bombs and mines cause the majority of deaths and injuries among U.S. and NATO forces in Afghanistan. Bombs made with small amounts of metal are difficult to detect.