Japan’s Air Self-Defense Force said Saturday that it conducted joint training with two U.S. Air Force B-52 heavy bombers over the Sea of Japan and East China Sea a day earlier, in what was seen as a show of force to both Beijing and Pyongyang.

The ASDF said that four each of its F-15 and F-2 fighter jets took part in the joint drill that was intended “to strengthen the deterrence and response capabilities” of the U.S.-Japan alliance.

The East China Sea is home to the Japan-controlled, China-claimed Senkaku Islands. China routinely sends government vessels to the area to assert its claims.

The joint air drills also come ahead of large-scale military exercises between the U.S. and South Korea set to kick off Monday. Both Tokyo and Seoul have raised the possibility of Pyongyang again launching a spy satellite sometime this month.

At a news conference Thursday, Chief Cabinet Secretary Yoshimasa Hayashi said Japan was watching the situation closely after South Korea’s defense chief claimed the North could launch a military reconnaissance satellite by the end of March.

"We will work closely with the United States and South Korea to collect and analyze the necessary information, and we will do our utmost to maintain vigilance and surveillance,” Hayashi said.

North Korea claimed to have successfully launched its first military spy satellite in November, and has said that it plans to launch three additional satellites this year.

Officials in Seoul have been dubious that the satellite is actually transmitting images, though some experts say it is “alive” after detecting changes in its orbit that suggested the North is successfully controlling it.