Malaysia's Federal Court on Tuesday reversed the acquittal of two policemen, finding them guilty of killing and blowing up a Mongolian model linked with a former associate of Prime Minister Najib Razak.

The officers, who were part of Najib's personal security detail at the time of the 2006 murder of 28-year-old Altantuya Shaariibuu, were initially found guilty in 2009 but were later acquitted in 2013.

The acquittal by the Court of Appeal, which ruled their conviction unsafe, had revived public outrage over the model's mysterious death and also appeared to distance the prime minister from the case.

On Tuesday, Malaysia's highest court unanimously ruled to overturn the lower court's decision and restore the High Court's conviction and death sentence.

The defense "had failed to cast reasonable doubt on the prosecution's case", said one of the five presiding judges, Suriyadi Halim Omar.

Malaysian law allows for review of Federal Court decisions, but it was not immediately clear if the defense would seek one.

"Obviously we respect the decision and will be bound by the decision," defense lawyer Kamarul Kamaruddin told reporters after the verdict.

Corporal Sirul Azhar Umar, 43 and Chief Inspector Azilah Hadri, 38, were found guilty on the basis of evidence that disputed their alibis and placed the latter at the crime scene.

The case attracted attention as the courts have never established a motive for the murder.

Sirul did not show up to face Tuesday's verdict. The court issued an arrest warrant for him.

In 2008, political analyst Abdul Razak Baginda, formerly a close associate of Najib, was acquitted of abetting the murder.

Civil society groups have alleged Shaariibuu's murder was linked to her role as an interpreter and associate of Razak Baginda in Malaysia's purchase of two Scorpene-class submarines from French shipbuilding giant DCNS in 2002.

Najib had previously denied allegations of links to Shaariibuu or corruption in the purchase.