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TEL AVIV, Israel - A humanitarian catastrophe looms in the Gaza Strip due to a lack of water, aid agencies warned as Israel intensified air attacks on Wednesday and ordered 100,000 Palestinians to evacuate border areas.

Airstrikes have caused massive damage to water and sewage infrastructure and have destroyed at least 560 homes, the U.N. Relief and Works Agency for Palestine Refugees (UNRWA) said as it declared an emergency in the area.

"Within days, the entire population of the Strip may be desperately short of water," Jacques de Maio, head of the International Committee of the Red Cross (ICRC) delegation in Israel and the occupied territories, said in a statement. If hostilities continue, just as temperatures soar in the region, "the question is not if but when an already beleaguered population will face an acute water crisis," he said.

Hundreds of thousands in #Gaza without #water. Within days, many more may find that there is no water when they turn on the tap. - Yves Daccord (@YDaccordICRC) July 15, 2014

"Water is becoming contaminated and sewage is overflowing, bringing a serious risk of disease," de Maio added.

At a news briefing, ICRC spokeswoman Nada Doumani said: "Water is a problem and it can quickly turn into a catastrophe.”

Israel’s security cabinet approved an escalation in military activity late Tuesday, hours after it abandoned an Egypt-brokered truce that was ignored by Hamas.

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Warplanes carried out dozens of airstrikes before dawn Wednesday, targeting 30 houses, four of them belonging to senior Hamas leaders including Mahmoud Zahar, according to the Gaza Interior Ministry website.

Wednesday's bombs brought the Palestinian death toll in the nine-day conflict to 209, with 1,550 wounded.

On the Israeli side, one man was killed Tuesday and several people were wounded - the first death in the Jewish state since the fighting erupted on July 8. The Israeli victim, Dror Hanin - who was killed by a mortar shell near the Erez crossing - was expected to be buried later Wednesday.

Hamas officially told Egypt Wednesday that it has rejected the propose truce, but Tuesday’s volley of rockets into southern Israel had already dashed hopes of a cease-fire.

Prime Minister Benjamin Netanyahu said Israel had "no choice" but to respond more forcefully. "Hamas chose to continue fighting and will pay the price for that decision," he said. "When there is no cease-fire, our answer is fire."

In addition to airstrikes, Israel ordered around 100,000 Gaza residents in the neighborhoods of Beit Lahiya, Shajayeh and Zeitun to evacuate. Leaflets dropped from planes, text messages and automated telephone messages were used to convey the warnings.

As part of our effort to avoid harming civilians, we are sending messages to residents of northern Gaza to leave homes for their own safety. - IDF (@IDFSpokesperson) July 15, 2014

“Whoever disregards these instructions and fails to evacuate immediately, endangers their own lives, as well as those of their families,” the leaflet warned.

Hundreds of residents of Zeitoun and Shijaiyah were seen walking in the streets, carrying small bags with belongings, but the Israeli Defense Force said Hamas had ordered civilians to ignore the warnings.

The IDF said 25 more rockets from Palestinian militants were intercepted by its Iron Dome interceptor system Wednesday. Air raid sirens sounded over Tel Aviv, where four rockets were intercepted.

Congress indicated support for longtime ally Israel Tuesday, backing a measure that would double the amount of money for Israel's Iron Dome missile defense system. The Senate Appropriations defense subcommittee approved a defense spending bill that would provide $621.6 million for Israeli missile defense, including $351 million for Iron Dome. "It works," said Sen. Dick Durbin, D-Ill., chairman of the subcommittee.

Meanwhile, Palestinian President Mahmoud Abbas - who reached an agreement with Hamas in April that led to the formation of a unity government last month - was expected to arrive in Cairo Wednesday for talks with Egypt’s President Abdel Fattah al-Sisi, the Palestinian leader's spokesman said.

The Associated Press contributed to this report. Alastair Jamieson reported from London.