Philippine President Rodrigo Duterte on Tuesday announced the termination of a two-decade-old Visiting Forces Agreement with the United States (VFA), delivering on threats to downgrade an alliance important to US interests.

The mercurial Duterte, who has clashed with the former colonial ruler over several issues, decided to pull the plug on the two-decade troop rotation pact to enable the Philippines to be more independent in its relations with other countries, spokesman Salvador Panelo said.

“The president will not entertain any initiative coming from the US government to salvage the VFA, neither will he accept any official invitation to visit the United States,” Panelo said in a statement.

The decision, sparked by the revocation of a US visa held by a former police chief who led Duterte’s bloody war on drugs, could complicate US military interests in the Asia-Pacific region as China’s ambitions rise.

It would also limit Philippine access to US training and expertise in tackling Islamist extremism, natural disasters and maritime security threats.

Panelo said Duterte’s decision was a consequence of US legislative and executive actions that “bordered on assaulting our sovereignty and disrespecting our judicial system”.

The US embassy in Manila called it “a serious step with significant implications”.

“We will carefully consider how best to move forward to advance our shared interests,” it said in a statement.

Given the importance of the alliance with the Philippines in broader US strategy, Washington still hopes the decision will be reversed or delayed before it takes legal effect in 180 days.

In Washington, a senior Trump administration official voiced disappointment over the decision.

“The United States shares a long history with the government and people of the Philippines and recognises that regional and global security is best served through the strong partnership that is enabled by the Visiting Forces Agreement,” the official said.

“We will continue to work with our Philippine government partners to strengthen this relationship in a way that benefits both our countries.”

The VFA is important to the overall US-Philippines alliance and sets out rules for US soldiers to operate in the Philippines. It underpins what Washington has called an “ironclad” relationship despite Duterte’s complaints about US hypocrisy, ill-treatment and ageing weapons.

Duterte says the United States uses the pacts to conduct clandestine activities like spying and nuclear weapons stockpiling, which he says risk making the Philippines a target for Chinese aggression.

Ending the VFA could hurt Washington’s future interests in maintaining 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.

‘We must have a say’

Some Filipino senators sought to block Duterte’s move soon after news of it broke, arguing that without Senate approval he had no right to unilaterally scrap international pacts it had ratified.

“We must have a say on this important matter,” said Senator Richard Gordon.

Some lawmakers are concerned that without the VFA, two other pacts would be irrelevant, namely the 2014 Enhanced Defence Cooperation Agreement made under the Obama administration and a 1951 Mutual Defence Treaty.

Those cover dozens of annual military training exercises and broaden the access of US forces and equipment to the Philippines, as well as bind the two countries to defend each other from external aggression.

Supporters of the agreements argue they have deterred Chinese militarisation in the South China Sea and US$1.3 billion of US defence assistance since 1998 has been vital in boosting the capabilities of under-resourced Philippine forces.

Philippine nationalists, however, say the United States did nothing to stop China building islands in the South China Sea equipped with missiles, and say the VFA is lopsidedly favourable to Americans, including the granting of immunity from prosecution for US servicemen.

Duterte, who favours closer ties with China and Russia, pressed ahead with the termination despite a Senate hearing on the VFA last week during which his senior generals and defence and foreign ministers spoke in favour of it.

- Reuters