THE country’s diplomats advised President Rodrigo R. Duterte about the risks of ending a US military pact on the deployment of troops for war games, but a decision had already been made.

“Secretary Locsin met with the President and US Ambassador Jose Manuel Romualdez but the President had already made up his mind,” Foreign Affairs Assistant Secretary Igor G. Bailen told a Senate hearing on Thursday.

Foreign Affairs Secretary Teodoro Locsin, Jr. earlier said he wanted a review of the visiting forces agreement (VFA) before ending it.

Mr. Duterte had threatened to end the pact after the US visa of Senator Ronald M. dela Rosa, his former police chief, was canceled.

Mr. Bailen also said the President could end the VFA without Senate concurrence.

“A plain reading of Section 21, Article 7 of the Constitution merely requires the concurrence of at least two-thirds of all the members of the Senate to make a treaty binding on the country,” he said.

“Were the frameworks of the Constitution had a different intention, they would have specifically and explicitly provided for the necessity for a similar concurrence by the Senate in the termination of or withdrawal from a treaty,” he added.

Mr. Bailen added that Mr. Duterte had “merely exercised his diplomatic powers granted to him by the Constitution” when he sent the termination notice to the US Embassy in Manila.

“As the power to enter into treaties is vested in the President, the power to terminate the same is incidental,” he added.

This led opposition Senator Franklin M. Drilon to question whether the President could also end other treaties and international agreements without Senate concurrence.

“The United Nations Convention on the Law of the Sea is the very basis of our entitlements to a 200-nautical mile exclusive economic zone in the West Philippines,” he said.

“Our baseline and other laws reflect this and other water marks. What if the executive department unilaterally decides to terminate the UNCLOS, will the Senate be left out from the conversation too?” he asked.

Administration Senator Aquilino Martin L. Pimentel III, who heads the foreign relations committee, said Senate Resolution 305 will serve as the upper chamber’s stand once a lawsuit is filed at the Supreme Court.

The Senate resolution filed by Mr. Drilon, “expresses the sense” of the Senate that the termination of treaties and international agreements approved by the Senate will be valid only upon Senate concurrence.

Mr. Pimentel said lawmakers can separately question the VFA termination before the Supreme Court if the entire chamber fails to adopt the Drilon resolution.

Mr. Duterte on Feb. 11 announced the termination of the two-decade-old VFA, which the US Embassy said was “a serious step with significant implications.”

Mr. Duterte’s decision, sparked by the revocation of a US visa held by a former police chief who led Mr. Duterte’s bloody war on drugs, takes legal effect in six months and US officials have expressed hope it can be reversed or delayed.

Mr. Duterte’s decision could complicate US military interests in the broader Asia-Pacific region as China’s ambitions rise.

Some Filipino senators have sought to block the move, arguing Mr. Duterte had no right to unilaterally scrap international pacts the country’s Senate had ratified.

The VFA is important to the overall US-Philippine alliance and sets out rules for US soldiers operating in the Philippines, a former US colony.

Washington has called the relationship “ironclad,” despite Duterte’s complaints that include allegations of US hypocrisy and ill treatment.

Ending the VFA complicates Washington’s efforts to maintain an Asia-Pacific troop presence amid friction over the presence of US personnel in Japan and South Korea and security concerns about China and North Korea.

Some lawmakers in the Philippines are concerned that without the VFA, two other pacts that make up the long-standing US alliance with Manila would be irrelevant, namely the 2014 Enhanced Defense Cooperation Agreement made under the Obama administration, and a 1951 Mutual Defence Treaty.

Salvador S. Panelo, Mr. Duterte’s spokesman, has called the VFA a one-sided deal that only benefits the US. — Genshen L. Espedido