ASEAN leaders are expected to voice concern over the heated territorial row between Japan and China over the Senkaku Islands when they hold their annual summit Sunday in Cambodia, a diplomat of the regional bloc said.

The diplomat, who spoke on condition of anonymity, said in an interview the heads of the 10-member Association of Southeast Asian Nations will urge Tokyo and Beijing "to undertake utmost restraint and to address the (Senkaku) issue through peaceful negotiation and dialogue with a view to ensure the maintenance of peace, stability and security in the entire region."

"The heads of state will express concern on the differences over competing territorial claims in the East China Sea," the diplomat said, alluding to the sovereignty of the Senkakus, which both China and Taiwan claim.