British Prime Minister David Cameron has urged Israel's Prime Minister Benjamin Netanyahu to do 'everything possible' to end the crisis in Gaza.
In a phone call with Netanyahu, Cameron also expressed sympathy for the 'unacceptable rocket attacks' Israel has suffered from militants.
About 40 Palestinians and three Israelis have now been killed.
Pro-Palestinian protesters gathered in Edinburgh and London to urge an end to the violence.
An Israeli air strike killed Hamas military chief Ahmed Said Khalil al-Jabari and another official in the Gaza Strip on Wednesday, the BBC reports.
The air strike followed a wave of rocket attacks into Israel from the territory.
A Downing Street spokeswoman said that Cameron also 'expressed concern' that the current trading of missile fire may turn into a ground war.
"The prime minister expressed his sympathy for the unacceptable rocket attacks that Israel continued to suffer," she said.
"He also expressed concern over the risk of the conflict escalating further and the danger of further civilian casualties on both sides," she added.
"The prime minister said that the UK was putting pressure on both sides to de-escalate and urged Prime Minister Netanyahu to do everything possible to bring the conflict to an end," she added.
Protesters earlier gathered outside the Israeli Embassy in London to condemn the British government's stance on the conflict.
Foreign Secretary William Hague has previously said that the Hamas regime in Gaza was responsible for the escalation of violence.
He urged both Israel and the Palestinians to make efforts to halt the growing conflict. (ANI)