The move has angered Israeli diplomats who say it breaches the terms of a deal last July when the four - who were serving life term - were to spend 18 months in a local prison before their release.

'Breakthrough deal'

Jordanian officials at the time said the deal was a breakthrough after years of negotiations with successive Israeli governments opposed to handing over Arab inmates deemed to "have blood on their hands".
   
They insist the deal allows an immediate release of the prisoners if Israel agreed to free Palestinians or Arabs serving life sentences for attacks in any future prisoner swap with Hezbollah or Hamas.

Israel accepted the deal as a gesture to Amman which in 1994 became the second Arab country after Egypt to sign a peace treaty with Israel.
   
The release reduces the pressure on the government, criticised by some for agreeing to a deal they see as humiliating.

Many Jordanians also see the prisoners as heroes resisting Israel's occupation of Arab land.

The country's opposition is lobbying for the release of another 30 Jordanians held in Israeli prisons on security related charges.