The world is "sailing a dark hour in our common history" with the Russian occupation of Ukraine, US President Joe Biden told Asian allies.
War is a "global issue", underlining the importance of protecting the international order, he said.
Biden is meeting with the leaders of Japan, Australia and India in Tokyo on his first visit to Asia as president, writes BBC
The four countries collectively known as the Quad are discussing security and economic concerns, including China's growing influence in the region, as well as their differences over Russia's war in Ukraine.
Japanese Prime Minister Fumio Kishida echoed Biden's comments and said a similar invasion should not happen in Asia.
India is the only Quad member so far that has refused to directly criticize Russia for the war. In her opening remarks at Tuesday's summit, Indian Prime Minister Narendra Modi did not mention the issue.21Media