A bomb blast ripped through the front of a crowded commuter bus as it passed the Israeli defense ministry in Tel Aviv during rush hour on Wednesday, injuring 17 people.

A spokesman for Prime Minister Benjamin Netanyahu said Israel had been hit by a "terrorist attack," with Washington calling it "outrageous" and Russia branding it as "criminal".

Palestinian President Mahmud Abbas hopes a Gaza truce will be announced Wednesday before U.S. Secretary of State Hillary Clinton ends a visit to the region, a senior official said.

"President Abbas told Clinton that Egypt was the key to everything," said Palestinian negotiator Saeb Erakat after a meeting in the West Bank town of Ramallah between Clinton and Abbas.

Iran bears a "heavy responsibility" in conflicts in the Middle East, especially in Gaza, French Foreign Minister Laurent Fabius said Wednesday.

Speaking specifically of Gaza, where a week of violence has claimed more than 140 lives, Fabius said: "There are long-range weapons up to 75 kilometers (45 miles) and these are Iranian weapons. Iran bears a heavy responsibility.

U.S. Secretary of State Hillary Clinton said in Jerusalem on Tuesday during Israel's conflict in Gaza that Washington's commitment to the Jewish state's security remains "rock solid."

But the top U.S. diplomat also stressed that Washington expected a quick de-escalation to a seven-day conflict that has shaken the already volatile region and now threatens to spill over into an all-out ground war.

U.S. President Barack Obama called Egyptian President Mohammed Morsi for the third time in 24 hours on Tuesday and "commended" his efforts to secure a truce in Gaza, the White House said.

"He commended President Morsi's efforts to pursue a de-escalation" in the Gaza Strip, deputy national security adviser Ben Rhodes told reporters traveling home from Asia with Obama during a stopover in Japan.

Two cameramen from Hamas-owned Al-Aqsa TV were among six people killed in Israeli air raids on the Gaza Strip, raising Tuesday's death toll to 20, a Hamas spokesman said.

Health officials said a total of more than 125 people had been killed and over 1,000 wounded since Israel began its relentless bombing campaign on November 14 in a bid to stamp out cross-border rocket fire by militants.

Israeli Prime Minister Benjamin Netanyahu told Gaza's Hamas leaders to choose between peace and "the sword" on Tuesday as a diplomatic push intensified to end a week of violence in and around the strip.

"Our hand is outstretched in peace to those of our neighbors who want to make peace with us," Netanyahu said in a statement.

Gunmen executed six "collaborators" in a Gaza City neighborhood on Tuesday, witnesses told AFP, adding that notices were pinned to their bodies saying they had been killed by Hamas's armed wing.

"Gunmen in a minibus pulled up in the neighborhood, pushed six men out and shot them without leaving the vehicle," one of the witnesses said, adding that a message pinned to the bodies read: "al-Qassam Brigades announces the execution of the traitors."

Egyptian and Hamas officials said they believed they could reach an agreement to end the week-long Gaza conflict on Tuesday but a truce hinged on Israeli assent to a Cairo-mediated ceasefire plan, as U.S. Secretary of State Hillary Clinton arrived in the region to make an urgent push for peace.

The emerging signs of a deal to end seven days of violence that have claimed the lives of 136 Palestinians came as the Israeli army confirmed its first two fatalities from rocket attacks while another missile landed harmlessly just south of Jerusalem.

Israel will "pay a heavy price" if it launches a ground operation in the Gaza Strip, Hamas's top military commander warned in a rare audio message broadcast on Tuesday.

"The enemy will pay a heavy price if it thinks of entering Gaza," Mohammed Deif said in the audio message carried by Hamas television station Al-Aqsa.