The Philippine foreign minister sparked a diplomatic fight over Twitter by asserting ownership over the Malaysian state of Sabah on the island of Borneo, reviving a longstanding territorial dispute between the Southeast Asian nations.

Malaysian Foreign Minister Hishamuddin Hussein, on his official Twitter account, said he will summon the Philippine ambassador on Monday in reaction to his Philippine counterpart’s July 27 tweet.

Philippine Foreign Secretary Teodoro L. Locsin, Jr., tweeted that “Sabah is not in Malaysia if you want to have anything to do with the Philippines,” reacting to a US Embassy item describing the area straddling both nations as part of Malaysia.

Sabah is a long-standing, on-and-off flashpoint between the neighbors, with the most recent flare-up in February 2013 when followers of a self-proclaimed sultan of Sulu, sought to claim sovereignty and led to clashes that killed dozens.

The sultans of Sulu once ruled over Sabah and the Sulu islands in southern Philippines. The state fell under British control after World War II and joined Malaysia in 1963, shortly after Sulu ceded its sovereignty to the Philippines.

The Sabah state itself is facing its own domestic political upheaval as the opposition party said it has enough majority in state parliament to take over—leading Chief Minister Shafie Apdal, who has also been touted as a possible prime minister candidate, to hold a lengthy meeting with the state governor late Wednesday amid talks of a snap state election. — Bloomberg