Hamas arrested three Palestinians who fired rockets into Israel from the Gaza Strip on Thursday, a militant faction said, in the first such detentions since the Islamist group and Israel agreed on a cease-fire last month.

Al-Aqsa Martyrs Brigades, a militant offshoot of President Mahmoud Abbas' Fatah faction, said Hamas men pursued its members after the attack and "abducted them" in Jabalya refugee camp.

"We demand their immediate release," said Abu Qusai, a brigades spokesman.

The cease-fire deal calls on Hamas to prevent cross-border rocket fire and attacks from the Gaza Strip and for Israel to halt its raids and ease an economic blockade of the impoverished territory.

Hamas official Sami Abu Zuhri said "we stress that all parties should maintain the national agreement that was reached with a consensus."

Hamas, which seized control of the Gaza Strip a year ago after routing forces loyal to the secular Fatah group, had previously said it would not use force against other militants who violate the truce.

Al Aqsa said it launched two Qassam rockets at the western Negev in retaliation for the Israel Defense Force's killing of an unarmed member of the group as he tried to cross a border fence into Israel earlier in the day. His death marked the first fatality along the Israel-Gaza border since the beginning of the Egypt-brokered truce on June 19.

An IDF spokesman said soldiers shot the man after he ignored their calls to stop and only saw later that he had been unarmed. The family of the victim, an 18-year-old youth, said he was probably looking for scrap metal along the border when he was killed.

The rockets struck open areas in the Sha'ar Hanegev Regional Council, causing no damage or injuries.

"If a total cessation of fire from Gaza, as committed in the calm, is not implemented, the calm has no possibility to succeed," Prime Minister Ehud Olmert's spokesman, Mark Regev, said.

More than a dozen rockets and mortars have been fired from Gaza since the truce began. In response, Israel has kept Gaza Strip crossings closed for about half the time, despite its pledge to gradually lift the siege of the coastal territory in exchange for calm.

Abu Zuhri said a Hamas delegation met Egyptian chief of intelligence Omar Suleiman in Cairo last night and urged Egypt to press Israel to stop closing crossings and to abide by the cease-fire.

Until Israel carried out its obligations under the truce deal, Abu Zuhri said, "there would be no chance" of resuming indirect talks on the fate of Gilad Shalit, an Israeli soldier seized by Gaza militants in a cross-border two years ago.

On Wednesday, Border Police troops operating undercover in the West Bank opened fire and killed a wanted Hamas man attempting to flee arrest.

Palestinians said two people were wounded in the incident in Kufr Dan, near the northern city of Jenin. They and two others were arrested, they said. The military had no immediate comment.

The truce does not extend to the West Bank, and Israel has been increasing its efforts to crack down on Hamas militants there. The operations have led to condemnation from the Palestinian Authority, which accuses Israel of hampering its local security efforts.

In the West Bank city of Nablus on Thursday, Israeli troops raided several charity organizations and a medical clinic and closed down a local television station apparently linked to Hamas, Palestinian officials said.

"The occupation's closure of some institutions will not delegitimise them ... and we will continue to deal with them," Palestinian Interior Minister Abdel-Razzak Yahya, referring to Israel, told a news conference.

Also on Thursday, a Palestinian health official said two Palestinians were killed in the collapse of a smuggling tunnel under the Gaza-Egypt border.

Health Ministry official Moawiya Hassanain said Thursday that five people were pulled out of the tunnel alive.

Local residents say the tunnel was used for smuggling drugs and fuel into Gaza.