MANILA (UPDATE) - Satellite images taken by an American think tank this month confirmed the presence of Chinese ships near Pag-asa island in the disputed South China Sea.

Images taken last August 13 by the Asia Maritime Transparency Initiative (AMTI) of the Center for Strategic and International Studies (CSIS) showed 9 Chinese fishing vessels and 2 Chinese Navy ships near Pag-asa island, part of Kalayaan town in Palawan that is home to a military detachment and a village.

AMTI said Thursday it is impossible to know if the ships are affiliated with China's maritime militia, but it noted that at least 2 of the ships appeared to be fishing with nets in the water.

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Chinese ship is seen near Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

A Philippine fishing boat is seen "docked at the nearest of the unoccupied sandbars" along Pag-asa island. Photo courtesy of Asia Maritime Transparency Initiative

Pag-asa (Thitu), part of the Spratly group of islands, is located about 480 kilometers west of Puerto Princesa City in Palawan.

Earlier this week, Magdalo Rep. Gary Alejano said he received information from his military sources regarding a "suspicious" convergence of Chinese boats north of Pag-asa island, which he claimed to be a threat to Philippine interest.

• READ: Presence of Chinese forces in Pag-asa 'suspicious', says Alejano

Foreign Affairs Secretary Alan Peter Cayetano on Thursday scored critics of the presence of Chinese vessels near Pag-asa island, saying China is not an enemy of the Philippines.

“Let me ask this: how many times have you asked me, bakit maraming American ship dun? You’ve never asked me that. Why? Because ang tingin ninyo, kaalyado natin ang US, kalaban natin ang China,” he told reporters.

AMTI said there also appears to be a Philippine fishing boat "docked at the nearest of the unoccupied sandbars" along Pag-asa island, which was possibly sent out to look into the presence of Chinese ships.

"The fishing vessels are all located between 1 and 5 nautical miles from Thitu (Pag-asa island), while the nearest military/law enforcement ship is about 3.6 nautical miles from the island. The ships are between 9 and 14.25 nautical miles from Chinese-occupied Subi Reef to the southwest," AMTI said.

The think tank said it was likely that authorities in China are aware of the activities of Chinese ships near Pag-asa island due to the presence of naval vessels.

"The number and rapid coordination of naval and coast guard ships suggests that this was purposely organized in advance and was not just an ad hoc response by government vessels that happened to be in the area," AMTI said.

The think-tank suspects that the "sudden and provocative" appearance of the vessels may be brought about by Beijing's desire to discourage Manila from constructing on Pag-asa island.

The Philippines has long been planning to rehabilitate the island's air strip.

Last week, AMTI also countered Cayetano's claims that land reclamation by China in the disputed South China Sea had stopped, releasing satellite images showing Beijing's continued activities on the disputed Paracel Islands.

• READ: China's land reclamation continues in disputed sea, U.S. think tank says

The Armed Forces of the Philippines (AFP) on Friday meanwhile said it was already addressing the issue of the presence of Chinese vessels near Pag-asa island.

"We will work to clarify all of these things and there is a mechanism that is built-in in our current relationship, which is called the Bilateral Consultative Mechanism that has already been initiated before," military spokesman Brigadier Gen. Restituto Padilla said.

Padilla said the military's Western Command has also been alerted to ensure the safety of Filipino fishermen in the disputed waters. He reiterated that sightings of foreign vessels such as that of China call for a diplomatic protest.

"We file diplomatic protest whenever we have sightings close to our areas. Especially this one," he said.

The latest sighting of Chinese ships followed the Association of Southeast Asian Nations' issuance of a communique earlier this month expressing concern for island-building and calling for non-militarization in the disputed waters.

• READ: ASEAN urges non-militarization in South China Sea