US Secretary of State Marco Rubio said China's recent use of water cannons against Filipino vessels in Scarborough Shoal is "disturbing".

"What's happened with the Philippines, you know, obviously, we saw that, too. The whole world saw it, and it's disturbing," he said in an interview with reporters Thursday on the sidelines of the ASEAN Foreign Ministers' Meeting in Pasay City.

Rubio noted that the "claims of sovereignty over territory are a growing challenge."

“That's why we continue to reiterate our commitment to our treaty partners, but also our commitment to freedom of navigation and respect for territorial rights in the region,” he said.

“It's one of the cornerstones of our engagement in the Indo-Pacific, and especially via ASEAN. And I made that point in every forum that we've had here,” he added.

Following the water cannon incident on Thursday, the Philippine Coast Guard and the Bureau of Fisheries and Aquatic Resources reported another harassment of China Coast Guard against Philippine vessels in the vicinity of Scarborough Shoal on Friday. This was the second straight incident in the area.

The CCG fired its water cannon against three Philippine government vessels carrying out the Kadiwa ng Bagong Bayaning Mangingisda program, an initiative of the national government to deliver fuel subsidies and provisions to Filipino fishing boats in Scarborough Shoal.

Aside from dangerous maneuver and shadowing, Rear Admiral Jay Tarriela, Philippine Coast Guard spokesperson for the West Philippine Sea said "a Chinese Maritime Militia vessel was also monitored pulling a rope approximately 100 meters dead astern of BRP Datu Sumakwel, an act that posed a hazard to the vessel's safe navigation"

"When a Chinese vessel drags a rope close behind one of our ships, the real danger is that the rope can get sucked into the propeller. Once that happens, the propeller jams, the engine can be damaged, and the ship is left floating helplessly in the middle of the sea — surrounded by Chinese vessels," he explained.

"A disabled ship that far from shore can no longer steer away from danger, can not complete its mission, and could even be towed or “rescued” by the Chinese, which is exactly the situation they want. And that is what makes this tactic sneaky: a water cannon attack is obvious to everyone, but a rope in the water looks harmless," he added.

Tarriela said as of 9:30 am, the PCG monitored a total of 26 vessels in the vicinity of Bajo de Masinloc: three PCG vessels, seven from the Bureau of Fisheries and Aquatic Resources, against 12 CCG ships and three Chinese Maritime Militia ships.

"The PCG strongly condemns the dangerous and unprofessional actions of the China Coast Guard. Bajo de Masinloc is an integral part of the Philippine territory, and its surrounding waters form part of- the country's territorial sea and exclusive economic zone," he said.

"The 2016 Arbitral Award has affirmed that Bajo de Masinloc is a traditional fishing ground of Filipino fisherfolk, whose rights cannot be lawfully impeded by any foreign power," he added. Robina Asido/PHS