The sixth day of the Gaza truce saw the first violations when three Kassam rockets slammed into Israel in response to the IDF killing of top Islamic Jihad operative Tarek Abu Ghally in Nablus on Tuesday. There was no immediate military response from the IDF. The rockets struck in the western Negev without causing any casualties or damage. Islamic Jihad claimed responsibility. "We cannot keep our hands tied when this is happening to our brothers in the West Bank," the group said in a statement. Hamas spokesman Sami Abu Zuhri said the rocket attack "came as result of Israeli provocation this morning." He added, however, that Hamas was "committed to the security calm." The first violation of the cease-fire came earlier, close to midnight Monday, when a mortar shell fired from Gaza hit the Negev. No one was hurt, and no damage was reported, and the IDF decided not to retaliate. No group claimed responsibility for the mortar fire. One official said it was highly unlikely that Prime Minister Ehud Olmert had signed off on the Nablus operation, or that Defense Minister Ehud Barak had approved it, since he was pushing for the Gaza cease-fire and it was clear that this type of action would endanger it. Olmert held consultations on the rocket fire when he returned from a meeting in Egypt with President Hosni Mubarak. One diplomatic source said it was now unlikely that Israel would increase the amount of goods allowed into the Gaza Strip, as the cease-fire plan entailed. Indeed, at Sunday's weekly cabinet meeting, Shin Bet (Israel Security Agency) head Yuval Diskin said the first test of the truce would come when the IDF carried out counterterror operations in the West Bank included either to the arrest or killing of members of the various terrorist organizations. Government sources expressed astonishment at the army's raid, saying it was a case of the right hand not knowing what the left hand was doing. One diplomatic official said there was no reason that Olmert would have had to sign off on the operation, since the IDF had already been authorized to carry out these types of raids without additional government's approval. Sources in the Central Command said the routine arrest raid had been approved at all the necessary levels. Two Islamic Jihad operatives were killed in the joint IDF-Shin Bet operation overnight Monday. The IDF said they died in exchanges of fire during an attempt to arrest them and that they had been planning to carry out a terrorist attack in Israel "in the very near future." Two years ago, the IDF and the Defense Ministry set up a mechanism according to which routine military operations would be approved at the highest levels during a period of diplomatic sensitivity. The IDF Spokesman's Office did not comment on whether that mechanism had been activated on Tuesday. It was clear, a government source said, that the Palestinians were trying to link events in the West Bank to the situation in the Gaza Strip, even though the agreement with Hamas explicitly said that the cease-fire was in Gaza Strip only and that Egypt would consider whether it could also be applied to the West Bank in another six months. The IDF Spokesman's Office said, "The IDF operates against terror in the West Bank in accordance with its authority and the necessary permits. The IDF does not conduct a dialogue with the political echelon via the media." Foreign Ministry spokesman Aryeh Mekel termed the Gazan rocket attacks "a grave violation of the cease-fire." AP and Jerusalem Post staff contributed to this report.