Chinese air force jets circled a Dutch frigate and approached a Dutch helicopter in the East China Sea in a way that “caused a potentially unsafe situation,” the Netherlands’ Defense Ministry said on Saturday.

In a statement, the Ministry said the HNLMS Tromp was patrolling on Friday in support of U.N. sanctions against North Korea when it was circled several times by two Chinese fighter jets.

Later, the ship’s NH90 helicopter was approached by two Chinese fighter jets and a helicopter.

“The incident took place in international airspace,” the ministry said. The Tromp is heading for Japan next and then to Hawaii for the “Rim of the Pacific” naval exercises.