A Vietnamese MiG-21 fighter jet crashed Thursday in the north of the country, killing the two pilots, a military source said. "The accident occurred around 14:00 after a very strong explosion," the officer from the Yen Bai provincial military command, 200 kilometres (125 miles) northwest of Hanoi, told a foreign news agency. "Two pilots were killed in the crash and there were no other victims on the ground," said the officer, speaking on condition of anonymity. Military authorities were investigating to determine the cause of the explosion and the identity of the victims.