The Philippines said Wednesday a politician who was once jailed for coup plotting had been in secret talks with China over a territorial row, as the tactic appeared to backfire amid bitter infighting.

Senator Antonio Trillanes had been "authorised" to hold back-channel talks with Chinese officials to settle a row over competing claims to Scarborough Shoal in the South China Sea, a spokesman for President Benigno Aquino said.

However the appointment caused a deep rift with Foreign Secretary Albert del Rosario, who had been officially in charge of negotiations with China and was excluded from the unofficial talks.

Trillanes claimed he had been responsible for easing tensions with China after the dispute erupted in April, and accused del Rosario of "treason" because of his allegedly aggressive tactics.

"Right now there is no more crisis involving Scarborough, but we were nearly brought to war. That was a treasonous act (by del Rosario)," Trillanes told AFP Wednesday, repeating a claim he made on local radio and to politicians.

He said public statements made by del Rosario accusing China of bullying the Philippines nearly led to open confrontation.

Trillanes said he had met "top Chinese officials" at least 15 times in Manila and in Beijing since May.

In a televised interview Monday, del Rosario said back-channel talks "were doing more harm than good", although he did not name Trillanes.

After the row spilled out to the local media, presidential spokesman Edwin Lacierda sought to limit the fall-out at a press conference on Wednesday.

"I can categorically say that the secretary of foreign affairs has the trust and confidence of the president," Lacierda told reporters.

However he said he could not answer questions as to why Aquino had appointed Trillanes as an extra negotiator.

Trillanes' appointment then became the top political story in the country when Senate president Juan Ponce Enrile launched a blistering attack on the former navy man in a nationally televised address.

Enrile, the third highest official in the country, said he backed del Rosario and accused Trillanes of undermining the Philippines' position with China.

"This guy is a fraud," Enrile said. "He told the Chinese we cannot impose our coastal protection." Trillanes walked out of the Senate, refusing to answer questions from Enrile.

The dispute between China and the Philippines began in April, when ships from both nations engaged in a stand off at Scarborough Shoal.

The shoal is an outcrop of rocks about 230 kilometres (140 miles) from the western coast of the Philippines' main island of Luzon. China claims nearly all of the South China Sea, even waters close to other Asian countries.

A former navy lieutenant, Trillanes was among the leaders of two failed coups in 2003 and 2007 against then president Gloria Arroyo.

He won a Senate seat in 2007 from a jail cell while on trial for rebellion. He was subsequently granted amnesty by Aquino, a fierce critic of Arroyo, before the trial ended.