The Israeli military has shut down the main roads around the Gaza Strip, a sign that it is poised to launch a ground offensive on the Palestinian enclave that could explode into an all-out war. Israeli airstrikes on the Gaza Strip early Saturday destroyed the Hamas Cabinet headquarters. The strikes followed an exchange of rocket fire Friday between Israel and Palestinian Hamas militants in Gaza with one Palestinian rocket landing in a field outside Jerusalem. Hamas claimed responsibility for the unprecedented attack on the holy city. Israel responded by calling up thousands more military reserves for a potential force of 75,000 reservists. Palestinian officials say 38 people have died in Gaza since the Israelis began the airstrikes earlier in the week. Three Israelis are reported to have been killed by Hamas rockets. Mr. Kandil said Egypt "will make sacrifices and every effort to achieve a truce." In Cairo, Egyptian President Mohamed Morsi called the Israeli assault a "blatant aggression against humanity." U.S. President Barack Obama telephoned the Egyptian president Friday to discuss the situation. Mr. Obama also spoke with Israeli Prime Minister Benjamin Netanyahu who thanked the U.S. for helping Israel develop a missile defense system that he says has knocked out hundreds of rockets, saving Israeli lives. An Israeli missile Wednesday killed the top military commander of Hamas in Gaza. Israel says the killing was in direct response to the almost daily rocket attacks on Israel from Gaza. Hamas vowed revenge and warned that Israel had opened up what