Israel will resist foreign pressure to halt its operations against Palestinian militants in the Gaza Strip, Prime Minister Benjamin Netanyahu said, according to BBC News.

He said Israel had attacked more than 1,000 targets there and was using twice the force it used during a similar operation in 2012.

Palestinian officials say at least 121 people have died in the air strikes. Hamas militants have continued to fire rockets into Israel from Gaza, causing damage and injuries.

Netanyahu said he had held "very good, positive" telephone consultations with U.S. President Barack Obama and German Chancellor Angela Merkel. But he added that "no international pressure will prevent us from acting with all power".

The Palestinian health ministry says in addition to those killed, 750 people - mainly civilians - have been injured in Israel's Operation Protective Edge since it began earlier this week.

The UN Office for the Coordination of Humanitarian Affairs has estimated that 77% of the people killed in Gaza so far have been civilians.

Israel says "dozens of terrorists" are among the dead.

UN High Commissioner for Human Rights Navi Pillay says there is "serious doubt" as to whether Israeli's military operation complies with international laws banning the targeting of civilians. "We have received deeply disturbing reports that many of the civilian casualties, including of children, occurred as a result of strikes on homes," Pillay said in a statement, according to the BBC.

Israel has repeatedly insisted that it tries to avoid civilian casualties, but says the militants often place their military assets in residential areas.