Doctors at a government hospital said on Friday the two Italians, Marti Albani and Pila Gee, received minor injuries in Thursday's blast.
A spokesman at the US embassy in Islamabad said the explosion also "slightly injured" a US diplomat who was having dinner with other US officials at the hotel. 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.
The explosion late on Thursday night at the heavily guarded hotel in Islamabad raised the level of tension in a country that has seen numerous attacks. But police and government officials said it appeared to have been an accident.
Sabotage ruled out
"There is no evidence so far of any terrorist activity or any [bomb] blast," Interior Minister Aftab Khan Sherpao told reporters at the scene.
He said an initial report by Pakistani explosives experts "ruled out the possibility of a sabotage".
"After preliminary investigations of the explosive experts, I can say with a lot of assurance that it was a short circuit that caused the explosion," he said, according to the state-run Associated Press of Pakistan news agency.
The explosion caused structural
damage to the hotel's entrance
"Due to short circuiting, gas accumulated in the empty space that created a vacuum, resulting in the explosion and causing burn injuries," Sherpao said.
The explosion also caused some structural damage at the hotel's entrance, he said.
Television footage showed blood and piles of shattered glass at the entrance to the luxury hotel, a haunt of visiting dignitaries and business personnel.
The hotel is in a part of the capital that is home to top government ministers and key offices.