Lance Corporal Joseph Scott Pemberton has been in prison since the October 2014 killing of Jennifer Laude, whom he met at a bar while on a break from military exercises in the northern city of Olongapo.

An Olongapo court ruled on Tuesday that Pemberton qualified for early release due to good behaviour while detained in a special jail at the Philippine military headquarters in Manila.

He has served half of a 10-year sentence for homicide.

His release has now been suspended after a sister of the victim challenged the ruling in a filing that asked the court to reconsider, Bureau of Corrections spokesman Gabriel Chaclag said.

Pemberton's lawyer Rowena Flores pressed for his immediate release.

"Every day that he stays in jail is a violation of his constitutional right," Flores told AFP.

Presidential spokesperson Harry Roque, a lawyer who represented the Laude family during the trial, said the court had committed "judicial overreach".

"Do not release him yet. The decision is not yet final and executory," Roque said.

Pemberton's conviction fell under the Philippines and United States' Visiting Forces Agreement (VFA), which covers the legal liability of US troops taking part in military operations in the Southeast Asian country.

President Rodrigo Duterte has shifted away from the US to pursue greater economic cooperation with China since assuming power in 2016. In February, he notified Washington that the Philippines would terminate the VFA for alleged US interference in his war on drugs.

But Manila later put the abrogation on hold, citing "political and other developments in the region".