Albanian officials said they believed the explosion was accidental, CNN reported.
Prime Minister Sali Berisha said that workers were dismantling the stockpile at the time. The depot near Tirana dates from the era of Stalinist dictatorship, and Altin Raijimi, an Albanian journalist, told CNN that some of the arms and ammunition may be 50 years old.
Albanian officials said that the dismantling operation was being done with a $30 million grant from the United States with supervision from a U.S. contractor, Rajimi told CNN.
Thousands of people were evacuated from villages near the depot.
The U.S. Embassy in Tirana issued a statement expressing sympathy with the victims of the explosion and offering to assist the Albanian government in dealing with the aftermath.