GAZA CITY, Gaza (CNN) -- A truce between Israel and Gaza's Hamas leaders will take effect Thursday and last for six months, Hamas officials said Tuesday. Palestinian Hamas security men stand to attention at a training academy in Gaza City last week. Israeli officials, however, stopped short of confirming that a cease-fire agreement has been reached. "It's still early to announce an agreement of calm," Israeli Defense Minister Ehud Barak said in a statement. "When it starts, if it starts, it's hard to say how long it will last. The test will be how it's implemented." Hamas senior official Mahmoud Zahar and Hamas negotiator Khalil al-Hayya announced the Egyptian-brokered agreement at a news conference in Gaza. They said it will begin at 6 a.m. Thursday (11 p.m. Wednesday ET).
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NEW: Hard to say how long any cease-fire will last, Israeli defense minister says
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Israel has not confirmed cease-fire pact
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Israel will begin to open Gaza border crossings Sunday, Hamas says
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Hamas took control of Gaza a year ago
Referring to the @placeholder mediation efforts, Barak said, "It's important to exhaust the possibility.