U.S. Secretary of State Antony Blinken told Southeast Asian leaders Friday that the U.S. is concerned about China’s “increasingly dangerous and unlawful” activities in the disputed South China Sea during an annual summit meeting, and pledged the U.S. will continue to uphold freedom of navigation in the vital sea trade route.

His comments at a meeting with the 10-member Association of Southeast Asian Nations’ drew swift condemnation from Beijing, which blamed U.S. and other military presences from beyond the region for instability in the waterway, which Beijing claims almost in its entirety.

China has overlapping claims with ASEAN members Vietnam, the Philippines, Malaysia and Brunei, as well as Taiwan. About a third of global trade transits through the sea, which is also rich in fishing stocks, gas and oil. A series of recent violent confrontations between China and Philippines as well as Vietnam have fueled concerns that China’s increasingly aggresive actions in the sea could spiral into a full-scale conflict.

Beijing has refused to recognize a 2016 international arbitration ruling by a U.N.-affiliated court in the Hague that invalidated its expansive claims, and has built up and militarized islands it controls.