MANILA (AP) ― Philippine President Benigno Aquino III on Saturday accused Chinese vessels of preventing Filipino fishing boats from seeking shelter at a disputed South China Sea shoal in new incidents that he said prompted his government to elevate the case to international arbitration.

Aquino told reporters on the sidelines of the World Economic Forum in Davos that the incidents took place recently at the Scarborough Shoal near the western coast of the northern Philippines. He said in one incident Chinese vessels got within 10 meters of two fishing boats and sounded their horns at full blast, and on another occasion two other Philippine boats were ordered out of the shoal despite bad weather.

Aquino quoted the fishermen’s account given to Philippine authorities.

The Chinese government did not immediately comment late Saturday.

Aquino, who was heading back to Manila from Davos, said the latest incidents in the South China Sea led his government to formally notify Beijing this week that it was bringing the countries’ dispute to a tribunal operating under the 1982 U.N. Convention on the Law of the Sea. It wants the panel to declare Beijing’s moves in the potentially oil-rich waters unlawful.

“So I think the record is very clear,” Aquino said. “We have tried to de-escalate the situation. We have tried to adhere to all of their requests ... help them with the transition period, and the transition, as far as we know, has already occurred. And instead of a de-escalation, there seems to be an escalation on their end,” he said. Aquino was referring to last year’s change of leadership in China, when according to Filipino diplomats, the Chinese side told their Philippine counterparts that Beijing was eager to settle the dispute.

Six governments have overlapping claims across the vast South China Sea, with China claiming it has sovereignty over virtually all of it. Chinese paramilitary ships confronted Philippine vessels last year in a monthslong standoff over the shoal that both countries claim.

In June, after the standoff, China wrested control of what it calls Huangyan island, and what the Philippines calls Scarborough Shoal. With a typhoon approaching, both sides agreed to withdraw their ships. But China quickly returned and strung up a cable across the lagoon to keep Philippine vessels out.

Aquino repeated his government’s position that the shoal ― a chain of tiny uninhabited horseshoe-shaped rocks 193 kilometers from the Philippine coastline ― is part of the Philippines’ 320-kilometer exclusive economic zone.

Despite the latest incidents, he said the Philippines is not going to complicate the situation and would wait for the next move of the U.N. tribunal.

Last week, the Chinese Embassy in Manila said that “China has indisputable sovereignty over the islands in the South China Sea and its adjacent waters.” It said that the disputes should be settled by the rival claimants through one-on-one negotiations.