The Philippines expressed concern over the presence of China‘s largest coast guard vessel within its exclusive economic zone (EEZ), viewing it as a troubling act intended to intimidate local fishermen near a disputed shoal in the South China Sea.

“We were taken aback by the escalating aggression displayed by the People’s Republic of China with the deployment of this massive ship,” stated Jonathan Malaya, spokesperson for the National Security Council, during a press briefing on Tuesday.

Manila has formally protested the presence of the 165-meter (541-foot) Chinese coast guard vessel 5901, which was located 77 nautical miles from Zambales province, and has called for its removal from the EEZ, according to Malaya. He characterized the situation as “an escalation and provocative,” asserting that the vessel’s presence is “illegal” and “unacceptable.” In response, the Philippine Coast Guard has dispatched two of its largest ships to escort the Chinese vessel away.

In a statement on Monday, Chinese foreign ministry spokesperson Guo Jiakun defended the coast guard’s actions, claiming that their “patrol and law enforcement activities” are “reasonable, lawful, and beyond reproach.”

Tensions between the Philippines, a treaty ally of the United States, and China have intensified over the past two years due to overlapping territorial claims in the South China Sea. An international tribunal ruled in 2016 that China’s extensive claims in the region lack legal foundation, a verdict that Beijing has dismissed. China’s claims encroach upon the EEZs of Brunei, Indonesia, Malaysia, the Philippines, and Vietnam, making the area a crucial shipping lane for approximately $3 trillion in annual trade.