MANILA (UPDATE) — The Philippine Navy on Monday expressed disapproval at China's latest radio challenge to Manila's coast guard.

According to Philippine Navy chief Vice Admiral Toribio Adaci Jr., Beijing is the one crossing the line and not the Philippines.

"I believed the scenario happened in the vicinity of Pag-asa Island and it's obvious who is crossing the boundary," he told ANC's "Headstart".

Asked if China should have not issued a radio challenge, he said, "That's my opinion."

Adaci added that the so-called code of conduct in the South China Sea could help deter aggressive action in Philippine waters.

"Nowadays, the maritime environment has become complex. Nations have resorted to the use of white ships, I'm referring [to] coast guard ships, to prosecute their territorial claims. That blurs the distinction between the navy and the coast guard," he said.

"We should give focus on external defense operation because... the challenge is really on our territorial waters," he added.

While there is no official directive yet on joint patrols with the US, Adaci said the Philippine Navy is prepared to undertake such mission.

• Amid tensions with China, Philippines gets bolder
• Joint patrols in South China Sea to begin 'very soon' - envoy

The Philippine Coast Guard has confirmed receiving a radio call challenge from the Chinese Navy while they were on their way to Pag-asa Island to distribute aid to residents.

"If you try to look at the claim features ng Philippines, Vietnam at China, halos magkadikit-dikit lang kasi siya. So, lalo 'pag gumamit ka ng eroplano, may possibility madaanan 'yung sinasabing territorial airspace nila. We respond [to] them through voice radio. We are telling them this is a normal routine," PCG Vice Admiral Joseph Coyme said in an interview.

(If you look at the claim features of the Philippines, Vietnam and China, they are situated closely together. So if you use an aircraft, there is a possibility of passing through the territorial airspace they claim.)

Manila's coast guard has been strengthening its defenses by placing buoys in the West Philippine Sea.

Coyme said the cardinal markers would serve as a warning or an alarm for seafarers that the direction is not advisable for navigation.

• Boya inilatag sa ilang bahagi ng West PH Sea bilang sovereignty markers

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