WASHINGTON (AFP) - The United States condemned a bus bombing that injured 17 people in Tel Aviv on Wednesday and undermined attempts to mediate a ceasefire in Gaza, branding it a "terrorist attack".

"These attacks against innocent Israeli civilians are outrageous," the White House said, reaffirming Washington's "unshakeable commitment to Israel's security and our deep friendship and solidarity with the Israeli people".

"The United States will stand with our Israeli allies, and provide whatever assistance is necessary to identify and bring to justice the perpetrators of this attack," it said in a statement.

Police said the blast erupted as the bus passed behind the Kiriya, Israel's sprawling defence ministry in the centre of Tel Aviv.

Television images showed the bus with its windows blown out and its metal frame contorted from the force of the blast, in images reminiscent of scenes from the second Palestinian intifada between 2000 and 2005.

The attack came as Hamas-controlled Gaza was rocked by new Israeli air strikes, and as US Secretary of State Hillary Clinton and United Nations chief Ban Ki Moon shuttled between Jerusalem and Ramallah trying to secure a ceasefire.

Just before the blast and after talks with Palestinian leader Mahmud Abbas, Mr Ban had appealed for an immediate halt to militant rocket attacks on Israel.