Some of the Palestinian rockets fired far into Israel during the Gaza flare-up have lacked powerful warheads because they were stripped down to increase range and spread alarm over a wider population, Israeli security sources said on Sunday.

"Our assessment is that the prestige of setting off alarms deep in Israel, and being perceived as fighting on, is as important to them now as spilling our blood," said an Israeli official briefed on security cabinet decisions.

The official and two other sources who spoke to Reuters on the matter did not specify how many of the almost 900 rockets and mortars fired since fighting erupted on Wednesday had been deliberately sapped.