The militant group Hamas said it remains committed to a cease-fire with Israel, but will not act as Israel's "police force" in confronting militants who breach the truce.
The comments by Hamas leader Khalil al-Haya came shortly after Gaza militants fired three rockets into southern Israel Tuesday, lightly wounding two Israelis. It was the first attack since the truce took effect last Thursday.
Israel responded by closing Gaza's border crossings, which are used to deliver food and basic supplies into the area.
Hamas said it was exerting pressure on Islamic Jihad, which claimed responsibility for the attack, to stop the rocket fire and demanded that Israel open the crossings. But al-Haya said its forces would not confront rocket launching squads on the ground.
'Working to implement the calm'
"Even if there is a violation by some factions, Hamas emphasizes its commitment to the calm and is working to implement the calm," al-Haya said.
"But Hamas is not going to be a police securing the border of the occupation," he added. "No one will enjoy a happy moment seeing Hamas holding a rifle in the face of a resistance fighter."
Israel called the rocket attack a "gross violation" of the Egypt-mediated truce. As part of the cease-fire, Israel had on Sunday begun incrementally increasing the amount of goods entering Gaza. On Wednesday, all cargo crossings were closed, though a pedestrian passage was kept open.
Hamas government spokesman Taher Nunu said the closure was a "clear violation of the calm" and called on Egypt, which mediated the truce, to intervene. "We will not accept leaving our people hostages to this policy," he said.
Militant commander killed
Islamic Jihad said the rocket attack was a response to an Israeli raid on the West Bank that killed an Islamic Jihad commander. The West Bank is not included in the truce. Islamic Jihad and other Gaza factions reluctantly agreed to the truce but were angered that the deal didn't include an Israeli cessation of West Bank operations.
Gaza and the West Bank are separate geographical entities located on opposite sides of Israel.
Islamic Jihad had said Tuesday after a meeting with Hamas that the rockets were an "exceptional" response to the West Bank fighting, suggesting that they would abstain from further rocket fire.
Many previous Israeli-Palestinian truces have unraveled in such ways, with minor violence gradually escalating and spiraling out of control. The sides committed to the truce for six months.
But both sides were eager to keep the fragile deal intact, with Hamas wanting to solidify its hold over the territory it overran last year by reopening the crossings and Israel hoping to bring quiet to southern areas where life has been paralyzed by the falling projectiles.
Later this week, Israeli and Hamas representatives are expected to travel to Cairo to work on the next stage of the truce: a swap in which Israel releases hundreds of Palestinian prisoners in exchange for a soldier held by Palestinian militants. Israel has balked at Hamas' demands, saying its list of prisoners is full of people involved in deadly attacks on Israelis.
The soldier, Sgt. Gilad Schalit, was captured in a cross-border raid on June 25, 2006. Discussion of the anniversary dominated Israeli radio programs on Wednesday, with Schalit's family and former Israeli prisoners of war sharing their stories.
Schalit's father, Noam, lamented that he has been unable to send notes to his son, and that a pair of glasses he tried to deliver through the Red Cross was returned. "We don't let ourselves think about these things. We are too busy with this fight," he said.
In Gaza, Abu Mujahid, a spokesman for the Popular Resistance Committees, one of the groups that captured Schalit, said Schalit is being dealt with in a "humanitarian way."
"We allowed him to send a message to his parents because we understand their pain and their feelings," he said. But he said the Palestinians would not ease their demands for the prisoner swap.
In violence Wednesday, an elderly man was shot along Gaza's border with Israel and moderately wounded, Palestinian doctors said.
The man, 81, was walking east of Khan Younis in southern Gaza when he was shot in the arm and hand. His family and Hamas accused Israel of shooting him. The Israeli army said it didn't know of any such incident.