The secretary general of the United Nations has expressed concern at the "terrible price" being paid by civilians in the wake of the escalation of hostilities on the Gaza border.

Since Friday a million Israelis have been forced to take shelter and have had their lives disrupted by rocket fire. More than 150 rockets have been sent by terrorists operating inside the Gaza Strip into Israel, causing injuries and damage to buildings.

Israel has retaliated with air strikes targeting terror cells that have left 18 militants and five civilians dead.

Ban Ki-moon said the rocket attacks were "unacceptable" but also called on Israel to "exercise maximum restraint". His comments were echoed by both Hillary Clinton, the US Secretary of State, and the Foreign Office. "I urge all sides to exercise restraint, re-establish calm and avoid any further civilian casualties," said Alistair Burt, the UK Minister for the Middle East.

The representative body of the British Jewish community also highlighted Israel's right to self-defence. In a statement, the Board of Deputies said the situation "for innocent Israeli civilians" in southern Israel was "unacceptable" and could not continue.

"We reaffirm Israel's right to self-defence and to protect her citizens from these acts of terror, as all right minded people should," they said. "We pray for all of the innocent victims."

The Israeli Prime Minister, Benjamin Netanyahu, said Israel would not cease striking at terrorist targets while the attacks continued. He warned those operating in Gaza that the IDF was "ready to broaden its operations and will continue to act as necessary."