By Martin Petty and Karen Lema
MANILA (Reuters) - Philippine President Rodrigo Duterte will meet Chinese counterpart Xi Jinping soon to discuss a 2016 arbitration case over the South China Sea, an aide said on Tuesday, as domestic pressure builds for the firebrand leader to stand up to Beijing.
Duterte has a consistent approval rating of about 80 percent but the same surveys show people in the Philippines mistrust China and want the government to fight its perceived maritime bullying.
Presidential spokesman Salvador Panelo said the leaders are likely to meet at the end of this month for talks that Duterte has said were his idea.
"'Remember that I said before that there will be a time when I will invoke that arbitral ruling?'" Panelo told a regular briefing, quoting Duterte.
"'This is the time. That's why I am going there' - that's what he said," Panelo added.
China's embassy in Manila did not immediately respond to a request for comment.
Duterte's move follows sharp criticism during his first three years in office for not pressing China to abide by a historic arbitration win, preferring instead to curry favour with Beijing.
That ruling in international law invalidated China's claim, based on its so-called nine-dash line, to historic sovereignty over most of the busy South China Sea waterway.
In exchange, Duterte received vague pledges of billion-dollar investment, most of which have yet to materialise. Opponents say Duterte has been duped.
Plans for the visit come as countries such as Vietnam, the Philippines and its ally the United States push back over the activities of the Chinese coastguard and a fishing militia that is thousands-strong in disputed areas of the South China Sea.
Last week, U.S. Secretary of State Mike Pompeo blasted Beijing for "decades of bad behaviour", in trade and at sea.
While Duterte continues to defend his policy of non-confrontation with China, his U.S.-leaning security top brass have spoken out strongly, indicating their patience with China is wearing thin.
Two diplomatic protests have been filed, the first over what the Philippines said was a recent "swarming" of more than 100 Chinese fishing boats near a tiny Philippine-occupied island.
The other concerned the unannounced passage in July of five Chinese warships through the Philippines' 12-mile territorial sea.
Duterte has been accused of gambling with sovereignty for repeatedly saying he had told Xi the Chinese were fine to fish in the Philippines' Exclusive Economic Zone (EEZ).
In June, a Chinese vessel smashed into a Filipino boat in the EEZ, stranding its 22 crew.
Panelo said Duterte wanted to discuss joint exploration of offshore energy reserves, a revival of a plan aborted almost a decade ago.
Separately, Duterte on Monday decided to end a practice of immigration officials refusing to stamp Chinese passports because maps in them feature the contested nine-dash line.
Instead, they will use a stamp that challenges the Chinese claim.
"The stamp has the map of the entire Philippines EEZ to the widest extent," Foreign Secretary Teodoro Locsin said on Twitter. "So tit for tat".
(Editing by Darren Schuettler and Clarence Fernandez)