The longtime treaty allies agreed in February to expand cooperation in "strategic areas" of the country as they seek to counter China's growing assertiveness over self-governed Taiwan and its building of bases in the South China Sea.

The 2014 Enhanced Defense Cooperation Agreement, known as EDCA, gave US forces access to five bases in the Philippines.

It was expanded to nine, but the locations of the four additional bases were withheld until Monday while the government consulted with local officials.

The four sites had been assessed by the Philippine military and deemed "suitable and mutually beneficial", the Presidential Communications Office said in a statement.

It added that the bases would also be used for humanitarian and relief operations during disasters.

A US official confirmed that the locations announced by the palace were the new EDCA sites.

Three of the sites are in the northern Philippines, including a naval base and airport in Cagayan province and an army camp in the neighbouring province of Isabela, the statement said.

The naval base at Cagayan province's Santa Ana is about 400 kilometres (250 miles) from Taiwan.

Another site will be on Balabac Island, off the southern tip of Palawan Island, near the South China Sea.

Cagayan Governor Manuel Mamba has publicly opposed having EDCA sites in his province for fear of jeopardising Chinese investment and becoming a target in a conflict over Taiwan.

But Philippine acting defence chief Carlito Galvez told reporters recently the government had "already decided" on the sites and that Mamba had agreed to "abide with the decision".

The agreement allows US troops to rotate through the bases and also store defence equipment and supplies at them.

The pact stalled under former president Rodrigo Duterte, who favoured China over the country's former colonial master.

But President Ferdinand Marcos, who succeeded Duterte last June, has adopted a more US-friendly foreign policy and has sought to accelerate the implementation of the EDCA.

Beijing has been critical of the agreement, which its embassy in the Philippines said recently was part of "US efforts to encircle and contain China through its military alliance with this country".

The Chinese embassy did not immediately respond to a request for comment.