The IDF carried out more than 35 air strikes in Gaza on Friday, killing four people and in another strike after darkness fell another 40 people were wounded some of them seriously, a Palestinian health ministry spokesman said.
IDF Spokesman Brig. Gen. Motti Almoz on Friday warned Palestinians in Gaza near weapons stockpiles to leave their homes.
"We are intensifying our attacks," he said, adding that Israel was "preparing for possible ground action".
Israel pulled its infantry and armored corps forces out of Gaza more than two weeks ago, after destroying much of Hamas' network of border infiltration tunnels.
But Prime Minister Benjamin Netanyahu granted preliminary approval on Thursday for the call-up of 10,000 army reservists, signaling the possibility of heightened military action in Gaza.
Friday's attacks brought the total number of targets hit by the IDF to some 200 since the ceasefire collapsed last Tuesday, and led to the renewal of rocket fire from Gaza and military strikes from the IDF, some of which targeted the heads of Hamas' military wing.
The IDF also said that 23 terrorists had been killed since the end of the ceasefire, including three senior Hamas commanders: Rafah Division commander Raed al-Attar, Southern Division commander Mohammed Abu Shmallah and Rafah Division senior commander Mohammed Barhoum.
Al-Attar and Shmallah were involved in the planning and oversaw the kidnap of IDF soldier Gilad Shalit in 2006.
Official medical sources in Gaza said that some 40 people were wounded in an Israeli attack Friday on an unknown target. Reports indicated that the attack had targeted a home in the southern area of Gaza City.
An unconfirmed number of Palestinians have also been killed since the return to hostilities.