AFP - An European Union parliamentary delegation on Thursday urged Israel to release long-term Palestinian prisoners.

"We believe that the release of prisoners... is central to the peace process," said Emer Costello, who headed the EU delegation on a three-day fact-finding mission on Palestinian prisoners held in Israeli jails.

The visit of four EU MPs came as Israel was mulling whether or not to release a final batch of long-term Palestinian prisoners under its commitments to US-brokered peace talks.

Israel agreed to release a total of 104 prisoners when talks kick-started by US Secretary of State John Kerry began in July.

It has freed 78 so far, but Israeli ministers have implicitly warned that should the Palestinians not agree to extend talks beyond their April 29 deadline, they will not release the remaining inmates as scheduled on March 29.

"We would certainly hope that those prisoner releases would continue and would take place. It is important as well that there are people in custody who are actually pre-Oslo," Costello said, referring to inmates who were supposed to be released under the 1993 Oslo peace accords.

"From the EU parliament's perspective... we (have) expressed major concern about the fact that there are currently 11 members of the PLC (Palestinian parliament) being held in custody... We would be seeking their release," she added.

Costello said Israel had barred the delegation from visiting the prisons, confining the trip to meetings with Israeli MPs and local rights groups.

Israel holds more than 5,000 Palestinians in its prisons, most of them on security grounds. Around 150 of these are held under administrative detention, without charge or trial, and another 150 are minors.