Two U.S. B-52 bombers flew with Japanese fighters in a show of support, amid pressure from China on Prime Minister Sanae Takaichi to back off on her remarks about Taiwan.

The joint U.S.-Japan exercise occurred on Wednesday, a day after China and Russia conducted a joint patrol with their warplanes in the seas around Japan’s southern islands, The Wall Street Journal reported. Three Japanese F-35s and three Japanese F-15s accompanied the B-52 bombers, the Japanese defense ministry said. 

“This bilateral exercise reaffirms the strong will between Japan and the U.S. not to tolerate unilateral changes to the status quo by force,” Japan’s Ministry of Defense said in a statement.

China and Japan have been quarreling since last month, when the Japanese prime minister said her country could be pulled into conflict over Taiwan to defend itself or its allies, like the U.S.

China has demanded Takaichi retract her statement, as it considers Taiwan a purely domestic affair, despite it being a self-ruled democracy. 

While Takaichi said she won't walk back her comments, noting that they were a statement of longstanding, if largely unspoken, Japanese policy, she has said that she won’t repeat them.

China has threatened reprisals against Japan, including possible economic measures such as banning imports of Japanese seafood and advising Chinese tourists to avoid the country. China’s Ministry of Foreign Affairs on Thursday repeated those warnings, citing earthquake risks after a quake on Monday in the sea off Japan’s northeastern coast.

Also, Chinese fighters locked radar onto Japanese planes that were sent to intercept them near Japanese airspace on Saturday, according to Japanese officials. Additionally, the Chinese Coast Guard and other vessels have repeatedly sailed close to the Senkaku Islands, which are Japanese territory that China claims as its own.