Israeli missiles targeted two buildings in Gaza early Monday, hours after Israel said it would step up its military operations until a young captured soldier is released.
CNN correspondent John Vause watched as a single missile flew over the roof on which he and his crew were standing in Gaza City; it slammed into a building a few blocks to the north, causing a powerful explosion.
The Israel Defense Forces and Palestinian sources said that al Aqsa Martyrs Brigades -- a military offshoot of Palestinian Prime Minister Mahmoud Abbas' Fatah movement -- had offices in that building.
The IDF also said it launched a missile attack on "a weapons production and storage warehouse in Beit Hanoun."
Monday's strikes came a day after an attack on the empty offices of Palestinian Prime Minister Ismail Haniya and a week after militants affiliated with Hamas captured 19-year-old Israeli Cpl. Gilad Shalit during a raid inside Israel.
At the start of his weekly Cabinet meeting Sunday, Israeli Prime Minister Ehud Olmert said Israeli security forces are under orders to do "all that is necessary" to bring about Shalit's return.
Olmert told his cabinet he had instructed the military "to intensify the force and activity of the IDF and the security elements in order to pursue these terrorists, those who send them, their ideologues and those who harbor them."
"No one will go unpunished," he said.
Saeb Erakat, an adviser to Palestinian Authority President Mahmoud Abbas, told CNN "more bombs are not going to bring the soldier back alive, nor will they resolve this complex situation. It will only add to the complexities."
Erakat and Abbas belong to the Fatah Party, which lost power to Hamas earlier this year. The Israeli offensive launched Wednesday includes the arrests of several members of the Palestinian government.
An Israeli helicopter gunship fired missiles on the building housing Haniya's offices in Gaza City early Sunday, and Israeli Deputy Prime Minister Shimon Peres told CNN the operation was carried out "to warn" Haniya.
"Either/or he is a government with all the responsibilities of a government, or it's a terroristic organization with all the consequences that stem from it," Peres said of Haniya on "Late Edition."
Israeli sources said Haniya's offices were being used by terrorists to plan attacks.
At the offices, Haniya said the attack was the product of "barbaric politics."
Abu Ubaida, spokesman for Hamas' militant wing, told the Reuters news agency, "If they continue with these attacks we will strike similar targets in the Zionist occupation which we have not targeted until now."
Ubaida later confirmed to CNN that he had issued the threat.
Two gunmen killed
Israeli Interior Minister Roni Bar-On told Israel Army Radio that Jerusalem was "tightening the pressure on Hamas."
"We want to ensure the fact that the kidnapped soldier would not be moved from the place we think he is in," Bar-On said.
"We wish to bring the soldier back home with minimum casualties, on our side and on the Palestinian side."
Israel launched two more airstrikes within an hour of the attack on Haniya's offices, both in or near the Jabalya refugee camp in Gaza, Palestinian sources said.
On Sunday evening, Israeli troops killed two Palestinian gunmen in clashes near the Gaza airport, the Israel Defense Forces and Palestinian sources said.
A day earlier, Israel Defense Forces clashed with Palestinian gunmen east of Khan Yunis, where Israeli intelligence officials say they suspect Shalit is being held.
Humanitarian aid allowed into Gaza
Israel opened two routes into Gaza on Sunday to allow for humanitarian aid to flow into the Palestinian territory, an Israeli army official said.
The Karni crossing in northern Gaza and a nearby fuel terminal at Nahal Oz were opened at midday to allow for the passage of food, medicine and fuel.
Israeli Defense Minister Amir Peretz said the Karni crossing would be open four days so trucks could carry humanitarian supplies into Gaza.
Olmert on Sunday called Shalit's captors "a bloodthirsty gang of terrorists who are causing us much suffering but who are mainly hurting the Palestinian population," according to a transcript posted on Olmert's Web site.
The prime minister said the military operation was not intended to hurt the Palestinian people, noting the opening of the Karni crossing.
He promised not to let the situation in Gaza -- where power has been sporadic since the Israelis bombed a power station, and where medical and food supplies are low -- devolve into a humanitarian crisis.
"We will do our utmost in this regard because we are not fighting the Palestinian population," he said.
Meanwhile, diplomatic efforts continued in an effort to secure the release of Shalit.
Abbas has been participating in the talks, and he was expected to meet Sunday in Gaza with the U.N. envoy to the Middle East, Alvero de Soto.
Omar Suleiman, head of the Egyptian Intelligence Services, was to arrive in Gaza as a mediator, Palestinian sources said.
Olmert spoke Sunday with U.S. Secretary of State Condoleezza Rice, "who telephoned in order to be updated on the situation in the Gaza Strip," Olmert's media adviser said in a written statement.
"She said that she was concerned by the deterioration in the humanitarian situation in the Gaza Strip and by the security situation."
Olmert told her that Israel had allowed 150 trucks carrying food and medical equipment to enter Gaza.
Three Palestinian militant groups have claimed responsibility for Shalit's abduction. Since Shalit's kidnapping, militants demanded that the Israeli government release Arab prisoners from Israeli jails. Israel rejected the request.