The Philippines' Department of Foreign Affairs (DFA) has issued a rare public rebuke to government officials and agencies over their public comments about China, stressing the need for a single, unified voice as the country prepares to host a major regional summit next week.

In a statement issued on Sunday, the department warned that remarks which cut across the government's diplomatic approach do more than complicate the work of its diplomats. "They risk eroding the country's credibility in international affairs and project an image of internal division that external parties can exploit," the DFA said. "Such actions can ultimately weaken the Philippines' negotiating position."

The statement was aimed in particular at the country's national security establishment and uniformed services, which have been engaged in months of heated exchanges with the Chinese Embassy on social media over incidents in the South China Sea, the busy waterway that Beijing claims almost entirely despite a 2016 international ruling that rejected the legal basis of its claims.

Tensions sharpened last month when several senators called for Beijing's ambassador to be declared persona non grata after he suggested China could "easily win" any confrontation with the Philippines. Beijing later accused Manila of "erecting multiple obstacles" to its attendance at a regional defence ministers' meeting, sending only an embassy defence attache in response.

The DFA said that while the armed services were indispensable in documenting maritime incidents, "civilian authority directs the country's international relations". It noted that the 2016 arbitration outcome, which broadly dismissed China's claims in the South China Sea, was achieved through "rigorous legal proceedings under international law, not through public messaging or social media".

The friction has also affected official contacts. Defence Minister Gilberto Teodoro was barred from visiting China this year, with Beijing citing what it called "irresponsible remarks".

Manila-based security analyst Chester Cabalza said the foreign ministry had gone public with its message to assure counterparts, particularly in Beijing, that it is in control of the Philippines' foreign policy. "The defence department and coast guard are obliged to carve out the security policy of the country but not its foreign policy," he said. "The DFA's statement is an assertion of their role in the bureaucracy."

The rebuke follows a telephone call last week between China's top diplomat, Wang Yi, and Philippine Foreign Secretary Theresa Lazaro. Wang urged the Philippines to rein in politicians who had "smeared" Beijing and crossed its "red lines". Lazaro described the conversation as "frank and constructive", adding that both sides emphasised continued dialogue and the careful management of differences based on mutual respect.

Manila is due to host the Association of Southeast Asian Nations (ASEAN) summit next week, with United States President Donald Trump and Brazilian President Luiz Inacio Lula da Silva among the leaders expected to attend. Beijing has yet to announce publicly who it will send.