Japanese and U.S. military forces held a joint disaster-relief drill Thursday at the U.S. Yokota Air Base in western Tokyo, the first exercise of its kind between the two nations.

The drill at the base, where the headquarters of the U.S. forces in Japan is located, played out a scenario in which a large number of people are injured from an explosion and subsequent fire at a U.S. base in Japan.

Six doctors and a helicopter from the Maritime Self-Defense Force and about 60 U.S. service members took part. The doctors simulated the examination of victims to determine those needing to be evacuated by helicopter to the MSDF's Yokosuka base in Kanagawa Prefecture.

The Defense Agency said the event was a standard disaster-relief drill, dismissing analysts' suggestions it was aimed at preparing for a possible terrorist attack.

Thursday's drill was part of major Japan-U.S. joint exercises being held throughout Japan for 17 days beginning Nov. 2. About 21,000 service members, 310 airplanes and 20 warships are taking part.

The Japanese and U.S. forces held their first joint evacuation drill Tuesday in Yamaguchi and Fukuoka prefectures to simulate a rescue of their nationals from foreign airports during a military conflict.

Tuesday's drill was in line with updated Japan-U.S. defense cooperation guidelines.