The Philippines asked China to refrain from acts that could disrupt the two nations’ improving relations amid simmering tension in the South China Sea.

“China should avoid performing acts that will place at risk the Filipino fishermen fishing in the disputed areas and at the same time cause irritants that will disrupt the current friendly relations,” President Rodrigo Duterte’s spokesman Salvador Panelo said in a statement late Friday.

The warning follows comments from China’s foreign ministry earlier on Friday, which said it hopes “non-littoral states will refrain from stirring up trouble in the calm waters of the South China Sea.” The Southeast Asian nation on the same day concluded its annual military drills with the U.S., which sent a fighter-jet-carrying warship for the first time.

Duterte, in a rare rebuke of China, earlier this month told Beijing to “lay off” from the Philippines-occupied Thitu Island in the South China Sea. Manila has escalated a protest over the presence of more than 200 Chinese vessels near the area.

Duterte’s spokesman also reminded China of the Philippines 2016 victory over China in The Hague, which ruled that there was no legal basis for China to claim historic rights to resources within seas falling within its nine-dash line.

“We remain steadfast in maintaining our claims with respect to our territory and exclusive economic zones,” said Panelo.