A massive explosion believed to have been caused by a rocket shook the Afghan capital late Wednesday near the U.S. Embassy compound, wounding an Afghan security contractor, officials said.

U.S. Embassy spokesman Lou Fintor said the blast did not occur on embassy property, and no Americans were injured. Staff rushed to a bunker in the compound after the 11 p.m. blast.

"All embassy personnel are safe and accounted for," Fintor told The Associated Press in a telephone interview.

A U.S. counterterrorism official, who spoke on condition of anonymity because it is still early in the investigation, said the southwest side of the U.S. Embassy's compound was among the buildings struck in the rocket attack.

The official was not immediately aware of casualties or the magnitude of the attack. It also was too early to say who was responsible.

Lt. Col. Todd Vician, a Pentagon spokesman, said one rocket struck near, but not inside, the U.S. Embassy compound, and no U.S. personnel were injured.

The blast occurred inside the grounds housing the state-run television offices, a police official at the scene said. The building is next to the heavily fortified embassy and the base for NATO-led forces in the capital.

The official, who spoke on condition of anonymity because he was not authorized to speak to the media, said the explosion apparently was caused by a rocket fired from southeast Kabul targeting the U.S. Embassy.

U.S. military spokesman Lt. Mike Cody said one Afghan security contractor was wounded, but he was unsure what caused the blast.

NATO-led troops in armored vehicles patrolled the area after the explosion.

"It was a very strong explosion near the ISAF (NATO's International Security Assistance Force) compound and we are trying to confirm its cause," spokesman Lt. Col. Riccardo Cristoni said.

The NATO force controls security in Kabul.

The explosion comes amid a spike in increasingly brazen attacks targeting U.S.-led coalition military forces in Afghanistan, particularly across the country's south, where remnants of the toppled Taliban government have carried out increasing numbers of bombings and attacks.

Militants occasionally fire rockets into downtown areas, and the threat of being kidnapped forces many foreigners to live in tightly guarded compounds surrounded by concrete bomb barriers and to travel in armored convoys.

In July 2005, a rocket slammed into the center of Kabul, exploding on a roadside near the U.S. Embassy and other diplomatic missions, but there were no casualties and little damage to nearby buildings.