Prosecutors at the Special Tribunal for Lebanon seeking to overturn the acquittal of two men over the 2005 assassination of Lebanese former prime minister Rafik al-Hariri said on Monday there had been "fundamental errors" in the judgment.

They said judges of the lower chamber had not properly assessed circumstantial evidence in the case, which was based almost entirely on mobile phone records, when they acquitted Hassan Habib Merhi and Hussein Hassan Oneissi last year.

"It is this incorrect approach to assessing the evidence which infects the judgment as a whole and is fundamental in understanding how, in the prosecution's submission, the judgment went wrong," prosecutor Norman Farrell said.

The lower trial chamber last year did convict a former member of the Shi'ite movement Hezbollah, Salim Jamil Ayyash, for the bombing that killed veteran Sunni Muslim politician Hariri and 21 others.

All suspects were tried in absentia and remain at large. Prosecutors are now seeking the conviction on appeal of Merhi and Oneissi.

Lawyers for Ayyash have also tried to appeal his conviction but appeals judges in April said there were was no legal framework to allow a defence appeal for somebody tried in absentia. Ayyash would be able to lodge an appeal or demand a retrial if he ever handed himself in, they said.

The hearing on the appeal lodged by the prosecution is scheduled to last five days. A judgment will follow later.

The Lebanon tribunal was created by a 2007 U.N. Security Council resolution. Funded by voluntary contributions and by the Lebanese government, the court said in June it was at risk of closing due to funding problems.

It says it has now secured enough funding to see the appeal in the Hariri assassination case through, but is expected to wrap up soon after.