TOKYO (Reuters) – Japan lodged a protest against Beijing on Friday after four armed Chinese coastguard vessels entered waters that Tokyo considers its territory.

The Japanese government said it was the first time that four Chinese vessels carrying what appeared to be cannon entered its territorial waters in the East China Sea surrounding the disputed islands, which Tokyo calls the Senkaku and Beijing calls the Diaoyu.

“I am not in a position to state what the Chinese side’s intentions are, but the intrusion of vessels belonging to China’s coastguard into (our) territory is a breach of international law,” Chief Cabinet Secretary Yoshimasa Hayashi told a press conference.

China’s coastguard said separately that it had patrolled the waters with vessels carrying weapons.

Tokyo lodged a “strong protest” through diplomatic channels calling for a swift exit from the area, Hayashi said. The four vessels stayed in the area for more than an hour and left shortly after midday, he said.

“The intrusion into our territorial waters is extremely regrettable and cannot be tolerated. We will continue to do our utmost to be vigilant and monitor the areas surrounding the Senkaku Islands with a sense of urgency, while dealing calmly and resolutely with China,” Hayashi said.

The two countries have repeatedly faced off around the uninhabited Japanese-administered islands.

China’s run-ins with the Philippine navy have also been escalating in disputed areas of the South China Sea.

(Reporting by Chang-Ran Kim; Editing by Alex Richardson)