The world is "navigating a dark hour in our shared history" with Russia's invasion of Ukraine, US President Joe Biden told key Asian allies.
The war has now become a "global issue" underscoring the importance of defending international order, he said.
Japanese PM Fumio Kishida also echoed his comments, saying that a similar invasion should not happen in Asia.
Mr Biden is meeting the leaders of Japan, Australia and India in Tokyo in his first visit to Asia as president.
The four countries known collectively as the Quad are discussing security and economic concerns including China's growing influence in the region - and differences over the Russian invasion.
Mr Biden's comments come a day after he warned China that it was "flirting with danger" over Taiwan, and vowed to protect Taiwan militarily if China attacked, appearing to contradict a long-standing US policy on the issue.
In his opening remarks at Tuesday's summit, Mr Biden said their meeting was about "democracies versus autocracies, and we have to make sure that we deliver".
The Ukraine war, he said, "is going to affect all parts of the world" as Russia's blockade of Ukraine grain exports aggravates a global food crisis.
Mr Biden promised the US would work with allies to lead the global response, reiterating their commitment to defend international order and sovereignty "regardless of where they were violated in the world" and remaining a "strong and enduring partner" in the Indo-Pacific region.
After their meeting, Mr Kishida told reporters that all four countries "including India" agreed on the importance of the rule of law, sovereignty and territorial integrity; and that "unilateral attempts to change the status quo by force will never be tolerated".
India is the only Quad member so far that has refused to directly criticise Russia for the invasion.
The Quad nations announced a new maritime monitoring initiative that is expected to step up surveillance of Chinese activity in the region, along with a plan to spend at least $50bn (£40bn) on infrastructure projects and investment over the next five years.
Formally referred to as the Quadrilateral Security Dialogue, the Quad began as a loose grouping of countries following the 2004 Indian Ocean tsunami that banded together to provide humanitarian and disaster assistance. The group fell dormant before it was resuscitated in 2017.
Since then however, the top leaders have gathered for the fourth time - they have already met once in Washington last September and twice virtually - in less than two years.
Analysts say the steady decline in each Quad nation's bilateral ties with China in the past few years appears to have given the grouping more impetus.
There has been mounting discomfort with China's growing assertiveness in the region, with ongoing maritime disputes between China and several countries, and a land boundary conflict with India.
Beijing's heavy investment in strengthening its navy and its recent security pact with the Solomon Islands has stoked fears in Australia, while Japan has become increasingly wary of what it calls routine "incursions" from the Chinese navy in its waters.
On Monday Mr Biden unveiled the Indo-Pacific Economic Framework for Prosperity (IPEF), a US-led trade pact aiming to promote regional growth that includes 13 countries, mostly in Asia.
US Commerce Secretary Gina Raimondo said it would provide countries "an alternative to China's approach". Officials said it would set standards in the areas of trade, supply chains, clean energy and infrastructure, and tax and anti-corruption.
The IPEF has been widely seen as a way for the US to re-engage with the Indo-Pacific after former US President Donald Trump's abrupt withdrawal from the Trans Pacific Partnership - a regional trade pact - in 2017.