Hamas says it has suspended negotiations on the release of Gilad Shalit, a captured Israeli soldier, because Israel was not respecting the terms of a truce with the group.

"It makes no sense for us to begin negotiating on the matter of Shalit's release when Israel is not committed to the calm," Moussa Abu-Marzouk, a senior Hamas official, said on Friday.

Israel sealed off the Gaza crossings again on Thursday in retaliation for a Palestinian rocket attack.

It was the sixth incident of rocket fire since a fragile Egyptian-brokered ceasefire deal came in force in Gaza.

Tenuous truce

The truce was supposed to lead to the easing of a crippling blockade Israel imposed after Hamas seized power in Gaza more than a year ago, but the military said the crossings would stay closed until at least Sunday.

In an interview with Al-Hayyat, a London based newspaper, Abu-Marzouk, chief negotatior on the fate of Shalit, accused rival Palestinian group Fatah of orchestrating the rocket attacks in order to sabotage Hamas.

Abu-Marzouk also called on Egypt to intervene to ensure that the rocket fire stops.

Israel has hinged its adherence to the ceasefire on negotiations for the release of Shalit, who was kidnapped by Gaza fighters in a cross-border raid in June 2006.

Israel is expected to free hundreds of Palestinians being held in its jails in exchange of Shalit.