William Hague has made a fresh appeal for restraint and a ceasefire in the Gaza crisis as the death toll mounted on the fifth day of heightened hostilities.
The Foreign Secretary warned Israel that it risked losing international sympathy if it escalated its campaign against Palestinian militants into a ground invasion.
But he repeated his insistence that Hamas bore "principal responsibility" for the violence and urged its leaders to cease a barrage of missiles still being fired at Tel Aviv and other areas.
Israeli prime minister Benjamin Netanyahu told his cabinet the Israel Defence Forces were prepared for a "serious broadening" of the operation - amid fears it will send in troops.
Several women and children were among 11 reportedly killed in an airstrike on a residential area as Israel expanded its targets to what it said were the homes of wanted militants.
There was also criticism of an attack on two media centres - with Hamas communications the alleged target - that wounded six local journalists and damaged international broadcasters' equipment.
Medical officials say 32 civilians are among 66 killed so far. Three Israeli citizens have also died.
"We are gravely concerned about this situation." Mr Hague told Sky News.
"We call on Hamas again to stop the rocket attacks on Israel, it is Hamas that bears principal responsibility for starting all of this and we would like to see an agreed ceasefire - an essential component of which is an end to those rocket attacks.
"The Prime Minister and I have both stressed to our Israeli counterparts that a ground invasion of Gaza would lose Israel a lot of the international support and sympathy they have in this situation."