MANILA - A foreign affairs analyst believes Defense Secretary Delfin Lorenzana's visit to the Pag-asa Island signals a stronger position of the Philippines on the disputed seas.

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Professor Richard Heydarian said Lorenzana's visit to the island located in disputed South China Sea is a "major, major shift" in the administration's moves regarding the matter.

This is the reason, said Heydarian, why China was "gravely concerned" and "dissatisfied" with the incident, prompting it to issue a statement.

"Now, we suddenly have the Duterte administration trying to draw the line in the sand and sending clearer signal to the Chinese that we're going to stand our ground," he told ANC on Monday.

Heydarian said Lorenzana's visit to Pag-asa Island shows that resistance is an option for the Philippines when it comes to the disputed seas.

He believes the Duterte administration should also make it clear that despite pledges of investments, the Philippines is standing its ground on its claims and is not giving concessions to China on the matter.

"I think it's very important for the Duterte administration to make it clear that improvement of bilateral relations is by no means tantamount to the Philippines just giving up on its claims and relaxing its position on sensitive territorial and maritime issues.," he said.

The Philippines and China are set to hold bilateral talks on the dispute in May.