The Philippines said it conducted maritime exercises in the South China Sea, a move that could escalate tensions in the disputed waters.

The coast guard said it deployed eight ships along with the fisheries bureau, as they trained on navigation, small boat operations, maintenance and logistical operations in Scarborough Shoal and Pag-asa Island. The maritime exercises come days after the Philippines fired diplomatic protests over the continued presence of Chinese vessels in a disputed reef.

“We are supporting the whole-of-nation approach in securing our maritime jurisdiction,” coast guard spokesman Armando Balilo said, adding it will also conduct medical missions with residents in Pag-asa Island next week.

Philippine President Rodrigo Duterte on April 19 said challenging China in the South China Sea will only lead to violence, and that he will only do so if Beijing drills for oil in the disputed waters.