The chief of the US Coast Guard has strongly criticized China's coast guard activities in the South China Sea for being inconsistent with the rule of law.

Commandant Linda Fagan spoke to reporters on Friday before the opening of an Asian security forum, the Shangri-La Dialogue, in Singapore.

Fagan criticized China apparently in light of a recent incident where Chinese coast guard ships used water cannons on Philippine patrol vessels in the South China Sea, causing injuries to the crew.

She stressed that the Chinese coast guard operates in ways that are inconsistent with the rule of law.

As for Japan's Coast Guard, she described it as a great example of a very capable one which her organization has built a long partnership with.

She said such a partnership would strengthen coast guards' abilities to respond to the problems in the region.

Observers say China is taking so-called "grey zone tactics" without using its military force, and showing increasingly assertive behavior in the South China Sea.

The United States is seeking stronger cooperation with coast guards of Japan and other friendly nations to counter China.