GAZA CITY, Gaza Strip (CBS News/CBSDC/AP) — A three-day cease-fire in the Gaza Strip went into effect Friday following heavy Israel-Hamas fighting that killed 17 Palestinians and five Israeli soldiers, but was almost immediately marred by reports of rockets from Gaza and the deaths of dozens of Palestinians from Israeli shelling.

In a worrying development for Israel, Hamas also claimed to have abducted an Israeli soldier in fighting near the southern Gaza border. If confirmed, it would be the first kidnapping since Israel’s current offensive began, and a major blow to the nation’s psyche.

Israeli Prime Minister Benjamin Netanyahu’s office said in a statement that, “once again, Hamas and the terror organizations in Gaza have blatantly broken the cease-fire to which they committed, this time before the American Secretary of State and the U.N. Secretary General.”

A senior Israeli official told CBS News the decision had been made to end the cease-fire, and blamed Hamas squarely for violating its terms by resuming rocket fire. Hamas denied breaking the cease-fire.

The truce, announced by the U.S. and the U.N. hours earlier, took effect at 8:00 a.m. local time (1 a.m. EDT) Friday. Negotiations on a more durable truce were supposed to take place during the lull under the terms of the deal.

U.S. Secretary of State John Kerry cautioned Thursday that there were “no guarantees” that the cease-fire would bring an end to the Gaza war, now in its fourth week.

As ever, Israel and Hamas both said they would respect the cease-fire but would respond to attacks, and Kerry’s cautionary note of the previous day proved well-founded just two hours into the halt in fighting.

A Middle East expert told CNN Friday that at least 3,000 members of Hamas’ elite fighting forces are prepared to carry out suicide attacks against Israelis.

“I was told by someone who had spoke to al-Qassam, the military wing of officer who said that before the ground operation began they were all instructed to go to their families and say goodbye to their families with the intent that they would not be returning alive from this battle,” Gershon Baskin, CEO and founder of the Israel/Palestine Center for Research & Info, told CNN. “This is one of the very difficult things about fighting with an organization like Hamas, particularly these very dedicated soldiers, combatants who are not afraid to die.”

Baskin continued: “And they believe that they are dying in the name of God; in the name of Allah; in the name of Islam; in the name of Palestine; and they do it with honor. It’s part of their duty to serve and they are deeply motivated to do this.”

A CBS News team approaching the Kerem Shalom border crossing at the far southern end of the Gaza Strip, from the Israeli side, heard explosions and was told by Israel Defense Forces (IDF) personnel that rocket fire was coming into the area from the Gaza side.

Soon after, Gaza officials said at least 40 Palestinians had been killed by Israeli shelling near the southern Gaza city of Rafah. Israel said it was looking into the reports, and confirmed there was “fear” an Israeli soldier had been kidnapped in the area.

In a statement, the IDF said, “at approximately 09:30 a.m. (2:30 a.m. Eastern), an attack was executed against IDF forces operating to decommission a tunnel. Initial indication suggests that an IDF soldier has been abducted by terrorists during the incident.”

Senior Hamas official Moussa Abu Marzok told CBS News the group had “captured one soldier and killed two.” Israel’s military confirmed two soldiers were killed in the clash near the tunnel entrance.

The White House said the abduction of an Israeli soldier would be an “absolutely outrageous” action by Hamas. Deputy national security adviser Tony Blinken told MSNBC the U.S. strongly condemned the alleged abduction, and called on Hamas to release the captive.

Blinken said Kerry was speaking to Netanyahu about the unraveling cease-fire.

Meanwhile, at least eight rockets landed in southern Israel Monday morning, causing some damage but no casualties, according to the IDF.

Terms of the cease-fire included a halt to rocket fire and a freezing of ground troop positions, according to CBS News correspondent Margaret Brennan. However, Israel’s operations to destroy Hamas’ elaborate tunnel network were expected to continue.

Israel said most of the 32 tunnels it had uncovered had been demolished and getting rid of the remainder would take no more than a few days.

The truce was announced hours after Netanyahu vowed to destroy Hamas’ tunnel network “with or without a cease-fire.”

Aides said Kerry made more than 100 calls over the last 10 days, including several dozen on Thursday alone, to broker the agreement that he failed to reach a week ago in Cairo to much ridicule and indignation from Israelis who accused him of going soft on Hamas. He announced the deal in the middle of the night Friday with an air of weariness, and solemnity, rather than declaring victory.

“This is not a time for congratulations and joy, or anything except a serious determination, a focus, by everybody to try to figure out the road ahead,” Kerry told a half-dozen reporters who were hastily summoned to his hotel suite only 45 minutes after the deal was struck. “This is a respite. It’s a moment of opportunity, not an end; it’s not a solution. It’s the opportunity to find the solution.”

U.N. spokesman Stephane Dujarric said the cease-fire was the result of Secretary-General Ban Ki-moon’s trip recent trip to the region as well as 48 hours of “extremely active diplomacy at all levels” – including Robert Serry, the U.N. special coordinator for the Middle East peace process.

At least four short humanitarian cease-fires have been announced since the conflict began, but each has been broken within a few hours by renewed fighting.

Hours before the latest cease-fire was to take effect, 17 Palestinians were killed in Israeli strikes, including 10 people from the same family, said Ashraf al-Kidra, a Gaza health official. He said the family members were killed in an airstrike on their home in the southern Gaza town of Khan Younis.

Israel’s military said five of its soldiers were killed along the Gaza border Thursday evening when a mortar round was fired at them.

A 15-year-old Palestinian boy told CBS News that he now wants to be a suicide bomber and blow himself up in Israel.

“The Israelis teach their children that we will kill them, so they take revenge on us,” Emran Krayka told CBS News.

Krayka added: “I will be a suicide bomber. I will blow myself up in Israel.”

More than 1,450 Palestinians have been killed since hostilities began July 8, according to Palestinian officials. Israel says 61 of its soldiers and three civilians in Israel have been killed.

In the hours before the cease-fire took effect Friday, Gaza police reported heavy Israeli tank shelling in northern and eastern Gaza, and the loud exchange of fire between Israeli troops and militants was audible throughout Gaza City. Tank shells landed on homes in the city, setting homes and shops ablaze.

Hamas fighters hit an Israeli tank with an anti-tank missile, Gaza police said, and then attacked Israeli troops who came to evacuate the tank crew. Clashes continued into the early morning hours, police said.

The Israeli military said it was looking into the matter.

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