MANILA - President Rodrigo Duterte will head for Beijing on Wednesday (Aug 28), his fifth visit since he took office in 2016.

While his previous visits have been more or less a love-fest between him and Chinese President Xi Jinping, this time their meeting promises to be less cordial.

Mr Duterte has said he will raise a 2016 ruling by an international tribunal on a case filed by the Philippines invalidating China's claim over most of the South China Sea.

He has resisted calls to press this victory in his first three years of his presidency, opting instead to curry favour with China. But now he is determined to bring it up, even if it touches a raw nerve in Beijing.

"Whether you like it or not, will make you (China) happy or not, angry or otherwise, I'm sorry. But we have to talk about the arbitral ruling," he said in a speech last week.

He revealed that certain quarters had pleaded with him to keep the ruling off the table.

"They said not to talk about it. I said, 'No'... Do not control my mouth because that is a gift from God," he said.

It is unclear just exactly what he hopes to achieve by bringing up the ruling now, midway into his six-year term.

China's top envoy in Manila, Mr Zhao Jianhua, has said Beijing's position on the matter - which is to ignore the ruling - is unlikely to change.

Predictably, Mr Duterte has said he does not want to pick a fight with China.

"We do not go to war. I will just feed my army and the military and the police to the mouths of hell," he said.

But this time, he wants China to go beyond just talk when it says it wants to resolve conflicts over the South China Sea peacefully.

"You just cannot talk air," he said.

Specifically, he wants to kick-start joint oil and gas exploration in contested waters.

"Let us talk about what is there. You have to share with us," he said.

China and the Philippines signed a memorandum of understanding to jointly explore resources in the South China Sea, and agreed to come up with something more concrete by November.

Mr Duterte is apparently getting impatient.

The Philippines is desperate for a new source of natural gas, as the Camago-Malampaya natural gas field is expected to dry up by 2024. The field off the coast of Palawan province fuels three power plants that provide electricity to half of the main island of Luzon.

Reed Bank, a shallow seamount that spans nearly 9,000 sq km, is a promising prospect. It is believed to hold up to 5.4 billion barrels of oil and 55.1 trillion cubic ft of natural gas.

But these resources are in waters that China and the Philippines are contesting.

China has agreed to a 60-40 resource sharing arrangement, in favour of the Philippines. Mr Duterte is pressing to have this set in stone.

His tougher posturing may also be intended to appease the military, analysts say.

In recent months, security officials have taken shots at Beijing over the sinking of a Philippine fishing boat by a Chinese trawler, "swarming" by China's fishing militia of a Philippine-held island, incursions by Chinese warships in Philippine waters, and friction caused by the burgeoning population of Chinese workers in Manila's offshore gaming industry.

Political analyst Richard Heydarian said: "Against the backdrop of rising criticism of China at home, Duterte is toughening his rhetoric to stave off a full-scale backlash."

But few expect Mr Duterte to push too hard and risk losing China as an ally.

"If anything, the visit to Beijing is likely to be an effort to ease tensions and explore new compromises," said Mr Heydarian.

Mr Gregory Poling, director of the Washington-based Asia Maritime Transparency Initiative, told the online news site Rappler that unless Mr Duterte's effort is part of a larger diplomatic effort to push back against China, "it won't make a difference".