Palestinian president Mahmud Abbas demanded in talks with US President Barack Obama that Israel free key Palestinian prisoners, including Marwan Barghuti, a Palestinian official said Thursday.

Earlier this month, Abbas said Palestinians will not agree to extend peace talks with Israel beyond their April 29 deadline without Israel releasing more prisoners beyond the fourth and final tranche planned for later this month.

During his meeting with Obama in Washington on Monday, "President Abbas demanded the release of more prisoners and Palestinian leaders in Israeli jails, like Saadat and Barghuti and Shubaki," manager of the Palestinian prisoner club Abdulal al-Anani told the official Voice of Palestine radio.

He was referring to Popular Front for the Liberation of Palestine (PFLP) leader Ahmad Saadat, former Palestinian Liberation Organisation finance official Fuad Shubaki and Marwan Barghuti, one of the main architects of the 2000 intifada.

Also on Thursday, an EU parliamentary delegation urged Israel to release long-term Palestinian prisoners, saying it was crucial to move a fragile Middle East peace process forward.

"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 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.

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.

The release of 78 long-term Palestinian prisoners since July has been welcomed by Abbas and by the public, especially jubilant families of the inmates, who saw their internment as political.

But it has angered bereaved Israeli families, whose relatives were killed at the hands of some of those released.

Peace talks relaunched last July have made next to no progress, marred by bitter disputes over core issues, and Washington is fighting an uphill battle to get agreement on a framework proposal that would extend the process to the year's end.