Israel is calling up 16,000 extra reservists to bolster its military in Gaza Strip.
The move comes as Israel pledged to investigate a strike on an UN-run school that killed at least 16 people, reports BBC.
The deployment brings the total called up by Israel to 86,000.
Officials told Israeli media the call-up gave the military "room to breathe".
Palestinian officials said more than 100 people in Gaza were killed on Wednesday.
Spokesman Mark Regev told the BBC Israel would apologise if it discovered that its fire was responsible for the strike on the school.
"We have a policy - we don't target civilians," he said.
The US and UN condemned the attack, with UN Secretary General Ban Ki-moon calling it "unjustifiable".
At least 1,360 Palestinians and 58 Israelis have been killed since Israel began Operation Protective Edge on July 8. Most aof them are civilians.
