"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.
- Netanyahu: First stop firing, then we'll talk
Mofaz: Gaza op long overdue, must continue
Another rocket fired at Tel Aviv area intercepted
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.
The official said "not a few" of the rockets reaching Tel Aviv and cities closer to Gaza were designed for much shorter ranges but had been shorn of their weighty warheads so that they flew further.
"They're pipes, basically," said the official, who declined to be identified.
Hamas had no immediate comment. The Popular Resistance Committees (PRC), another outgunned Palestinian faction taking part in the five days of clashes, dismissed the Israeli allegations.
"Israeli leaders are trying to assure their terrified public that those rockets are not dangerous, to minimize their fear. They will never succeed, and time will tell they lied to their people," PRC spokesman Abu Mujahed said.
Israeli Air Force and artillery strikes on Gaza have killed some 56 Palestinians, most of them civilians. Palestinian rockets have killed three civilians and wounded dozens of others in Israel since Wednesday, driving entire populations into bomb shelters.
Tel Aviv has become a target from the air for the first time since 1991, when Saddam Hussein's Iraq fired Scud missiles at Israel's biggest city. A rocket also crashed near Jerusalem for the first time in four decades.
The enemies have hotly disputed the condition of Gaza's most potent rockets, with Israel saying its air force has destroyed the bulk of them on the ground and the Palestinians insisting they were continuing to strike at the heart of the Jewish state.
For the fourth time in as many days, rockets were launched at Tel Aviv, some 70 kilometers (44 miles) from Gaza, on Sunday. The salvo, claimed by Hamas, set off sirens in Israel's coastal commercial hub and suburbs. The Iron Dome interceptor shot down two rockets.
A third source who receives regular briefings from Israel's air defense corps said some of the furthest-reaching Palestinian rockets had warheads that were lighter than they were designed to have.
"Yes, this was to increase range, but we have no indication of rockets without warheads being used," the third source said.
Israel's military and police declined comment.
The discrepancy between the Israeli disclosures could be due to the difficulty of studying rocket debris left over from Iron Dome interceptions, or the possibility that not all of the sources were privy to intelligence data on Palestinian tactics.
Hamas said the rockets it has fired at Tel Aviv were Iranian-designed Fajr-5s, with ranges of 75 km (46 miles) and 175 kg (385 lb) warheads that can shear through buildings.
But there has been no word of direct impacts in Tel Aviv. The rockets were either blown out of the sky by Iron Dome or, according to some witnesses, fell harmlessly into the sea.
If any did land in unpopulated areas, the locations were not disclosed by Israeli authorities, in order to deprive the rocket crews of any information that could help them adjust their aim. Iron Dome is designed to intercept any rocket or mortar on course to hit a populated area.
Hamas also launched, on Friday, a rocket that it dubbed a homemade "Qassam M-75" at Jerusalem, which has no Iron Dome shield. That launch set off sirens throughout the holy city and some witnesses reported hearing an explosion to the south.
Police have not published extensive details on the incident.