BRP Sierra Madre, a vintage ship, is "strongly anchored" and cannot easily be removed from Ayungin Shoal, a Philippine Navy official said after confirming the presence of a Chinese tugboat in the vicinity of waters of the shoal on Monday.

The ship was run aground by the Navy at the shoal in 1999 to show that the Philippines has sovereignity in the area. China has been asking the Philippines to remove the BRP Sierra Madre.

"The monitoring by the Philippine Navy and the AFP for the past days have noted the presence of a tugboat only yesterday. While this is not a cause for alarm, it is also not a reason for us to be prepared for them to tow away BRP Sierra Madre," Rear Admiral Roy Vincent Trinidad, Philippine Navy spokesman for West Philippine Sea (WPS), told reporters in Camp Aguinaldo on Tuesday.

"That cannot be done easily because BRP Sierra Madre is firmly anchored there. It is strongly anchored on corals. Yes. It will take more than a tugboat to pull out Sierra Madre," he added.

Trinidad said as of Monday, the number of Chinese vessels in the vicinity of Ayungin Shoal "went down to 13 maritime militia, two coast guard vessels and one People's Liberation Army Navy tugboat."

"The average distance (of Chinese vessels) right now is two to 2.5 nautical miles away from Sierra Madre," he said.

Trinidad said based on their assessment, China will use the tugboat to pull out their own vessels in case it runs aground in the shallow portion of the shoal, noting the recent attempt of Chinese boats to come near the BRP Sierra Madre.

"Our assessment is that this is more for their own use in the event that they would need a tugboat to pull out any of their ships that would run aground in the shallow portion of Ayungin Shoal," he said.

"There was at first an attempt of two speedboats and one (rigid hull inflatable boat) RHIB to come close to Sierra Madre, which eventually they left. And then followed by a speedboat that tried to come closer, but two of our RHIBs was able to block them and to drive them away and they complied," he added.

Trinidad also stressed that aside from the death of a Filipino due to the coercive and aggressive actions of Chinese vessels, pulling out the BRP Sierra Madre is also one of the "red line" considered by the AFP.

"The commander-in-chief mentioned that the death of a Filipino will be grounds for invoking the (Mutual Defense Treaty) MDT. This was amplified by the chief of staff of the AFP. This is now a red line. Any death of a Filipino due to the coercive and aggressive actions of the (China Coast Guard) CCG, the PLA Navy, and the Chinese maritime militia is a red line for the Armed Forces of the Philippines," he said.

"Of course. there are already rules of engagement and contingency plans in place for any eventuality it includes that (attempt to pull out BRP Sierra Madre)," he added. Robina Asido/DMS