Prime Minister David Cameron has voiced his support for Israel and its response to what he calls “appalling” rocket strikes from Hamas militants.
The Israeli army has stepped up its offensive on the Gaza Strip in an effort to hit Hamas targets, as militants continue to fire rockets at Israeli cities.
Mr Cameron phoned Israeli leader Benjamin Netanyahu on Wednesday to offer his support.
A Downing Street spokesman said: “(He) spoke to Prime Minister Netanyahu earlier this evening about the situation in Israel.
“The Prime Minister strongly condemned the appalling attacks being carried out by Hamas against Israeli civilians.
“The Prime Minister reiterated the UK’s staunch support for Israel in the face of such attacks, and underlined Israel’s right to defend itself from them.”
In response to the escalating conflict, the United Nations Security Council is set to convene in New York on Thursday.
“Gaza is on a knife-edge,” UN Secretary-General Ban Ki-moon said.
“The deteriorating situation is leading to a downward spiral which could quickly get out of control. The risk of violence expanding further still is real.”
The exchange of fire marks the heaviest fighting between Israel and Hamas since an eight-day battle in November 2012.
The IDF launched the major air campaign above Gaza on Tuesday, targeting the homes of suspected militants and concealed rocket launch locations.
More than 400 airstrikes have taken place, with 50 people killed in Gaza.
Israel said it had hit more than 300 targets and Hamas positions throughout Gaza.
The Israel Defence Force (IDF) said “at least 82 rockets hit Israel” on Wednesday, and 21 were intercepted.
Hamas said it fired three rockets on Wednesday at Dimona, targeting what Israel claimed was its highly secure nuclear reactor site.
There have been no Israeli deaths, but the barrages have paralysed business in southern communities.
Mr Netanyahu has warned Hamas that it will pay a “heavy price” for the rocket attacks, many of which have targeted populated areas of Israel.
The Israeli cabinet has said it may also send in ground troops and has authorised the call-up of as many as 40,000 reservists.
Palestinian President Mahmoud Abbas has accused Israel of committing atrocities in Gaza.
Mr Abbas said: “It’s genocide – the killing of entire families is genocide by Israel against our Palestinian people.”
The US State Department said it has called for all sides to deescalate, but reiterated Israel’s right of self-defence.