MANILA - In an escalation of a Twitter row, Philippine Foreign Secretary Teodoro Locsin Jr. on Thursday said he would summon the Malaysian ambassador in Manila over comments the latter's foreign minister made on his tweet that "Sabah is not in Malaysia."

• Malaysia to summon PH envoy over Locsin's 'Sabah is not in Malaysia' tweet

Locsin fired fresh tweets Thursday morning in response to Malaysian Foreign Minister Hishammuddin Hussein, who called his post on Sabah on Monday “irresponsible,” saying it “affects bilateral ties.”

The Philippines has laid a subdued claim over Sabah, a territory part of Malaysia’s northern Borneo, citing a land lease agreement in 1878 between the Sultanate of Sulu and the British North Borneo Chartered Co.

"No country can tell another what it can and cannot say about what the latter regards as rightfully its own," Locsin wrote, asserting his right to lay Manila's sovereign claims.

"I don't insist China say only what we want to hear about the Arbitral Award. It is free to say what it wants while we say and do what needs doing. That holds for Sabah," Locsin said, referring to the Philippines' arbitral victory that invalidated China's 9-dash line claim over the disputed South China Sea and which Beijing continues to reject.

"And that's China we're talking about—the second biggest economy and military power in the 21st century. I am summoning the Malaysian ambassador," he added, tagging his department's official Twitter handle, @DFAPHL.

And that's China we're talking about—the second biggest economy and military power in the 21st century. I am summoning the Malaysian ambassador @DFAPHL. https://t.co/Bcd66luGBN

— Teddy Locsin Jr. (@teddyboylocsin) July 30, 2020

Citing his meetings with two Chinese ambassadors "time and again to talk about our differences, sometimes heatedly but always forthrightly," Locsin said he "never objected to China making contrary claims, nor China to me doing the same with our uncompromising stand."

"That's diplomacy," he said.

Hey idiot, two Chinese ambassadors and I have met time and again to talk about our differences, sometimes heatedly but always forthrightly. I never objected to China making contrary claims nor China to me doing the same with our uncompromising stand. That's diplomacy. https://t.co/x0TBZ4tuK6

— Teddy Locsin Jr. (@teddyboylocsin) July 30, 2020

The virtual exchange that has led to a diplomatic incident puts the spotlight on a rarely discussed territorial row between the Southeast Asian neighbors.

Just last year, on a visit in Manila, then Prime Minister Mahathir Mohamad said "there is no claim" when asked of the Philippines' assertion of sovereignty over Sabah in an exclusive interview with ABS-CBN News.

In response, the Philippines said there is a claim.

Since June, the Philippines has been transporting Filipinos from Sabah, a territory governed by Malaysia just southwest of Sulu, back to their home provinces as part of measures to help undocumented Filipinos facing the COVID-19 crisis.

This was the subject of Locsin's tweet on Monday, where he reacted to a US Embassy post on aid it has provided for "returning Filipino repatriates from Sabah, Malaysia."

The US Embassy has not deleted or amended the tweet despite Locsin's callout. It has not responded to a request for comment.

There has only been intermittent discussions between the Philippines and Malaysia over their competing claims on Sabah, and the latter has continued to govern the territory.

In November 2016, President Rodrigo Duterte and then Prime Minister Najib Razak agreed to set aside the dispute.

In 2013, hundreds of militants from Tawi-Tawi went to Lahad Datu in Sabah to assert their claim, calling themselves "Royal Security Forces of the Sultanate of Sulu and North Borneo.”

Malaysia has sentenced 9 Filipinos to death over the incident.

• READ: Philippines will never abandon Sabah, Spratlys claim: Locsin