Israel announced on Wednesday that it had converted 30 percent of Gaza's territory into a buffer zone as it pressed its unrelenting military offensive, vowing to maintain its blockade on humanitarian aid to the war-ravaged territory.

Israel resumed air and ground attacks across the Gaza Strip on March 18, ending a two-month ceasefire with Hamas that had largely halted hostilities, with rescuers on Wednesday saying at least 11 were killed in strikes across the Palestinian territory.

The UN said an estimated 500,000 Palestinians have been displaced since the end of the Gaza ceasefire, triggering what it described as one of the most severe humanitarian crises the territory has faced in more than 18 months of war.

The Israeli military on Wednesday said that as part of its resumed operations, it had "achieved full operational control over several key areas and routes throughout the Gaza Strip".

"Approximately 30 percent of the Gaza Strip's territory is now designated as an Operational Security Perimeter."

It added that Israeli air strikes had hit "approximately 1,200 terror targets" and that "more than 100 targeted eliminations have been carried out" since March 18.

Defence Minister Israel Katz had declared earlier this month that the military was seizing "large areas" of Gaza, leaving it "smaller and more isolated."

Top Israeli officials have repeatedly claimed that military pressure was the only way to force Hamas to release the 58 hostages still held in Gaza. (AFP)