Germany said Israel had a "right to self-defence" against deadly rocket fire by Palestinian militants.
"The German government condemns these incessant rocket attacks from the Gaza Strip against Israeli cities in the strongest terms," Chancellor Angela Merkel's spokesman Steffen Seibert said Wednesday.
"Israel has the right to self-defence against these attacks."
European Union chief Charles Michel called on Israelis and Palestinians to halt fighting and avoid civilian casualties, after speaking with Israeli president Reuven Rivlin.
"Very worried by the recent upsurge of violence and indiscriminate targeting. Priority should be de-escalation and prevention of the loss of innocent civilian lives on both sides," European Council President Michel said on Twitter Wednesday.
The chief prosecutor of the International Criminal Court voiced concern at the escalation of violence between Israel and the Palestinians and said "crimes" may have been committed.
"I note with great concern the escalation of violence in the West Bank, including East Jerusalem, as well as in and around Gaza, and the possible commission of crimes under the Rome Statute," which founded the ICC, Fatou Bensouda said on Twitter Wednesday.
The United States urged both Israel and the Palestinians to avoid "deeply lamentable" civilian deaths, calling for "calm" after days of violence.
"Israel does have a right to defend itself. At the same time reports of civilian deaths are something that we regret and would like to come to a stop," State Department spokesman Ned Price said Tuesday.
"We don't want to see provocations. The provocations we have seen have resulted in a deeply lamentable loss of life," he said.
"We continue to call for calm, continue to call on all sides to de-escalate and to exercise restraint in their actions."