Israel and Hamas continued exchanging fierce attacks Saturday as Israeli forces massed along the Gaza border in preparation for a possible ground invasion.

Israel carried out more than 200 air strikes on the Hamas-ruled Gaza Strip Saturday, destroying the Hamas Cabinet headquarters, while Palestinian rocket fire continued as far north as Tel Aviv.

Israel's military has shut down main roads around Gaza, a sign it could be poised to launch a ground offensive. Israel's Cabinet has authorized the mobilization of up to 75,000 reservists. Tanks and other armored vehicles are also positioned along the border.

Meanwhile, the Israeli military says its new “Iron Dome” missile defense system shot down a rocket bound for Tel Aviv, one of several Hamas has fired at Israel's commercial center.

Israel says “Iron Dome” has intercepted nearly 250 of the hundreds of rockets fired at Israel since the conflict began a few days ago.

One rocket landed Friday in a field outside Jerusalem.

There has been no serious talk of a cease-fire.

Palestinian officials say nearly 40 people have died in Gaza since the Israelis began their airstrikes earlier in the week. Hamas rockets have killed three Israeli civilians.

Tunisia's foreign minister visited the Gaza Strip Saturday. Rafik Abdesslem is the second high-profile visitor to Gaza since the latest wave of violence. Egyptian Prime Minister Hesham Kandil visited on Friday.

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.”

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 has opened up what it calls “the gates of hell.”

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