The U.S. Embassy warned Americans on Friday to stay away from Islamabad's Marriott Hotel after an explosion that wounded seven people, amid skepticism over Pakistani officials' explanation that it was caused by electrical short-circuit, not a bomb.

The embassy warning did not say whether there was any evidence the Thursday night blast, which shattered the building's glass facade, was an attack. It urged caution, however, and said embassy employees were forbidden from going to the hotel until further notice.

The explosion at the heavily-guarded hotel increased the level of tension in a country that has seen numerous terrorist attacks, and the quickness with which Pakistani officials declared the blast an accident raised eyebrows.

"Nobody believes it was an electrical short-circuit," said a Western diplomat on condition of anonymity.

Only minutes after the blast, a parade of senior Pakistani officials, including the information and interior ministers, insisted it was caused by a short-circuit in an air conditioning unit in the ceiling near the hotel entrance.

On Friday, they said they still had no reason to believe it was caused by anything but an accident.

"We searched and investigated everything minutely and found no clue to term it a sabotage attempt," Ehsan Sadiq, the head of the police investigation team, told Pakistan's state news agency. "It is simply a short-circuit that blasted through the air conditioning pipe."

Islamabad Police Chief Fayyaz Ahmed Toor (search) was removed from his post Friday, but it was not clear if the move had anything to do with the hotel blast.

Among the injured were two Italians and a U.S. diplomat, authorities said Friday. Doctors at a government hospital said the two Italians, Marti Albani and Pila Gee, received minor injuries.

A spokesman at the U.S. embassy in Islamabad said the diplomat was having dinner with other American officials at the hotel, and that he was also slightly injured. The diplomat's name was not immediately released.

The spokesman, who did not want to be named, said the injured diplomat is at his home in Islamabad.

The rest of the injured were Pakistanis. Most were listed in stable condition.

Television footage showed blood and piles of shattered glass at the entrance to the luxury hotel, a center for visiting dignitaries and businesspeople. The hotel is in a part of the capital that is home to top government ministers and key offices.

The Marriott and other upscale hotels in Pakistan are extremely well guarded, with barricades and armed guards who check all vehicles for bombs.