Demonstrations against Israel's military action in Gaza and in support of Palestinians took place in Tehran and 700 other Iranian cities after Friday Muslim prayers, news agency ISNA said.

Protesters chanted "death to America" and "death to Israel" in the capital, in demonstrations called for by the authorities.

French President Francois Hollande said Friday he was seriously concerned by the escalation of violence in the Gaza Strip and had spoken to Israeli and Egyptian leaders a day earlier.

"I am seriously concerned by what is happening in the Gaza Strip, both by the rocket attacks on Israel and the reprisals that this escalation may bring," Hollande told reporters at a joint press conference with Poland's President Bronislaw Komorowski, who called for a resumption of peace talks between Israel and the Palestinian Authority.

Egyptian Prime Minister Hisham Qandil vowed Friday to intensify Cairo's efforts to secure a truce and end Israel's "aggression" in the Gaza Strip.

"Egypt will not hesitate to intensify its efforts and make sacrifices to stop this aggression and achieve a lasting truce," he said at a press conference in Gaza City's Shifa hospital after seeing some victims from the latest Israeli strike.

Gaza fighters fired rockets at both Jerusalem and Tel Aviv on Friday aiming for the Jewish state's political and commercial hearts, prompting Israel to call up thousands more reservists in readiness for a potential ground war.

The military wing of the Islamist Hamas movement which rules Gaza said it fired the rocket at Jerusalem, the first to strike the outskirts of the Holy City in the history of the Israeli-Palestinian conflict.

The Israeli army started calling up 16,000 reservists on Friday, as officials said the Jewish state was preparing for a possible ground offensive into the Gaza Strip.

"They're distributing emergency call-up notices now, the process has started," an army spokeswoman told Agence France Presse.

The United States is calling on Egypt to use its sway with the Palestinians to try to end the violence from Gaza, a top U.S. official said Thursday, adding Hamas must stop its rocket attacks on Israel.

"We ask Egypt to use its influence in the region to help de-escalate the situation," deputy State Department spokesman Mark Toner said, adding that Secretary of State Hillary Clinton had spoken with her Egyptian counterpart.

Russian President Vladimir Putin on Thursday urged both Israeli Prime Minister Benjamin Netanyahu and the Palestinians to avoid escalating Gaza violence that has killed 15 Palestinians and three Israelis.

"The president of Russia called on the parties to exercise restraint and avoid the path of escalating violence, whose victims include civilians, and to do everything to return the situation to its normal course," the Kremlin said following a telephone conversation between Putin and Netanyahu.

Israel will take "whatever action is necessary" to defend its citizens from Palestinian rocket attacks, Prime Minister Benjamin Netanyahu said on Thursday as Gaza's Hamas rulers noted that the current conflict “will shorten the era of occupation.”

Netanyahu's remarks at a televised press conference in Tel Aviv came after Israel carried out 24 hours of air strikes on Gaza, killing 15 Palestinians, at least seven of them Hamas militants.

Former Prime Minister Saad Hariri slammed on Thursday the Israeli assault against the Gaza Strip, saying that it demonstrates the “hostile policy of Israel against the Palestinians and Arab people in general.”

He said in a statement: “The occurrence of the attack simultaneously with the ongoing Syrian revolution poses questions over its timing and is a sign of the clear intentions to thwart the revolt as much as possible.”

British Foreign Secretary William Hague said Thursday that Hamas "bears principal responsibility" for the surge in deadly Gaza violence, saying it should cease attacks against Israel immediately.

He also strongly urged Israel to do its utmost to reduce tensions, avoid civilian casualties and help create the conditions for peace, warning: "It is imperative to avoid the risk of a spiral of violence."