The U.S. military C-130 airplane crashed late Thursday near the remote village of Rovie, in the Drizez Mountains, about 60 miles southeast of the capital, Tirana.
Albanian army Chief of Staff Lt. Gen. Pellumb Qazimi said the plane was taking part in a joint exercise with Albanian forces.
"The military, police and local population are taking part in the search effort — it will be exhaustive," Qazimi said. "The incident occurred during a military exercise between the two countries in very bad weather conditions."
He said the dead were all American.
The plane crashed in a small forest near Rovie. The crash site was cordoned off by U.S. military personnel.
The U.S. European Command in Stuttgart, Germany, said the cause of the crash was being investigated but did not comment on the fate of the crew, saying the "status of the individuals on board is yet to be determined."
It said the military transport was assigned to the 352nd Special Operations Group, at Mildenhall in England.
Albanian officials said they did not believe anyone survived the crash.
"If there were survivors we would have learned of it by now," Defense Ministry spokesman Agim Doci said.
Members of Albania's special forces and U.S. helicopters based in neighboring Kosovo were assisting in the search effort.
Albania, seeking eventual membership in NATO, has close ties to the U.S. military. It backed the American-led campaign in Iraq, where it has deployed a small unit of 71 troops. Albania also has peacekeeping contingents in Afghanistan and nearby Bosnia.
The U.S. ambassador to Albania, Marcie B. Ries, thanked Qazimi for the search effort.
"This is an example of the excellent cooperation existing between the United States and Albania," Ries said. "We are very grateful for the tremendous support from the Albanian military."