The Philippine armed forces said Japan and Australia “expressed willingness” to take part in joint maritime patrols with it and the US in disputed waters.

“Other countries who are open to the idea will be identified later,” Armed Forces of the Philippines spokesman Col. Medel Aguilar said in a text message to reporters.

The military said Saturday it’s escalating maritime surveillance after detecting a “resurgence” of Chinese vessels around the West Philippine Sea, parts of which are being claimed by the country, China and other Southeast Asian nations.

The Philippines has held joint military and naval drills with the US, Japan and Australia amid tensions with China in the resource-rich West Philippine Sea.

The US military on Thursday said it wants to gain access to additional Philippine sites to tighten a defense alliance between the two countries. The US earlier this year was given access to four more sites under the 2014 Enhanced Defense Cooperation Agreement, which initially covered five Philippine military bases. The new sites are located near Taiwan and the South China Sea.

Read: US Military Says It Wants Access to More Philippine Sites