Tensions from long-standing territorial disputes spilled over during the annual meeting of Southeast Asian leaders despite China’s efforts to put a lid on the issue.

A charged atmosphere replaced the usually jovial mood Monday when Philippine President Benigno Aquino III questioned Cambodian Prime Minister Hun Sen when he tried to cut off a discussion of the territorial row, AP reports. Cambodia, the host of a series of summits, had previously claimed that the bloc had agreed not to raise the issue.

Mr. Aquino insisted Cambodia does not speak for ASEAN and that “as a sovereign state, it is our right to defend our national interests”. Mr. Aquino stood by his stance that countries need to clarify their territorial claims in accordance with international law.

China denied accusations that it had manipulated the agenda by using Cambodia and defended its key ally, Financial Times reports. “Cambodia’s efforts are to safeguard the unity of the ASEAN,” Foreign Ministry spokesman Qin Gang said.

Beijing lashed out against the Philippines and Vietnam for breaking the regional consensus with their outspoken response, and went on to blame Japan for the recent clashes over disputed islands in the East China Sea.

It also asserted that it would deal with rival claimants bilaterally and blamed the nations for disturbing peace and stability in the region.

President Barack Obama urged the countries to show restraint and called for a multilateral solution. Washington reiterated its neutral stance on the territorial dispute but said it would not allow the use of force.