HAGATNA, Guam (AFP) - An explosion at a bar in the Guam Hilton on Thursday left two people injured and resulted in the Pacific resort's evacuation, officials said, as United States security agencies investigated the cause of the blast.

The Guam Fire Department said the cause of the blast, which occurred around 8.30pm local time at an outdoor bar in the Hilton, was unknown, with the Federal Bureau of Investigation and Homeland Security both investigating.

Department spokesman Ed Artero said it was too early to say whether the the explosion was an accident or an attempted attack on US territory, which is home to som 6,000 military personnel, including Marines, submariners and bomber crews.

"We have no theory at this point. It's still under investigation, but everything is under control," Mr Artero told AFP.

He said two people - a 32-year-old male Japanese tourist and a 33-year-old local female - were rushed to the Guam Memorial Hospital but their injuries were not serious.

Japan's Foreign Ministry confirmed that a Japanese man was slightly injured.

"There was an explosion. We know that a male individual received very minor injury," a Tokyo-based diplomat told AFP, saying staff from the consulate general's office on Guam had spoken with the man.

The ministry was not aware of any information indicating the explosion was a terror attack, he said.

A Honolulu-based FBI spokesman confirmed: "The FBI is cooperating with the Guam authorities in investigating the explosion."

He referred further queries to the Guam police, who were not returning calls.

There was also no response from calls to the Hilton.