MANILA – A week after saying it will be "possible but difficult" to impeach President Rodrigo Duterte, Magdalo Rep. Gary Alejano on Tuesday said the firebrand leader may face ouster if he fails to protect Benham Rise from Chinese incursion.

"Kung mayroong impeachment na ifa-file, that’s a culpable violation of the Constitution. Iyung ating territory, dapat pinapangalagaan natin. Kapag pangulo na mismo [ang] nag-violate, he should be [held] accountable," Alejano said.

Alejano, an ally of Senator Antonio Trillanes IV, was reacting to reports quoting Duterte that he won't take China to task for its ships' presence in Benham Rise.

• READ: Duterte says he won't fight China over presence in Benham Rise

"While [Defense Secretary Delfin Lorenzana] sees the incident as ‘very concerning,’ to Mr. Duterte, ito ay wala lang. He even said that he gave permission to the Chinese to enter the area. Are we going to let China fool us again in Benham Rise in 2017 onward?” the lawmaker asked.

The Philippines should be transparent regarding all its dealings with China, he said, because what the country exchanges with China might be more than the cost of “a few billion dollars in loans and grants.”

He also said the government should “denounce in strongest terms” the intrusions of China in the Philippines’ sovereign territory, based on articles of the United Nations Convention on the Law of the Sea (UNCLOS) limiting their entry.

Alejano maintained that the Philippines could defend its territory, which includes Benham Rise.

Earlier on Tuesday, the government asserted its right to Benham Rise, following China’s claim that the Philippines cannot declare it as its territory, despite a 2012 UN ruling.

"Benham Rise belongs to the Filipino people. The Philippine government is duty-bound to defend and protect the sovereign and territorial right of this region," Presidential spokesperson Ernesto Abella said in a press briefing.

• READ: PH rebuffs China: Benham Rise is ours

• READ: PH can't claim Benham Rise as its territory – China

"Other countries can exercise innocent passage and territorial navigation, but they are disallowed to stay and establish any structure in the area."

This came a day after Duterte said he preferred talking to China regarding the presence of Chinese ships in Benham Rise, and believed China would not build structures there.

"Why would I want to fight? I'd rather talk…I cannot match the might of China. Have you seen how they are prepared to fight terrorism?" Duterte said.

Chinese foreign ministry spokesperson Geng Shuang confirmed Monday that Chinese vessels recently passed through Benham Rise for "marine research," but insisted this was only in exercise of the principle of "freedom of navigation" and "right to innocent passage."