The addition brings the total number of reservists Israel has called up since the beginning of the operation againstHamas to 86,000, a military spokeswoman said.
The conflict has killed more than 1,300 people in Gaza, according to the Ministry of Health in Gaza. Most of the dead are civilians, the United Nations has said.
Fifty-six Israeli soldiers have died, according to the Israel Defense Forces, and three civilians have been killed in Israel.
After more than three weeks of fighting, Israeli Prime Minister Benjamin Netanyahu said Thursday that Israel would complete its goal of destroying Hamas' network of tunnels with or without a cease-fire. Netanyahu said this is just the first phase of the demilitarization of Gaza.
While U.S. officials have called on Israel to do more to protect civilians, the United States has agreed to Israel's request to resupply it with several types of ammunition, a U.S. defense official told CNN on condition of anonymity. It's not an emergency sale, the official said.
Among the items being bought are tank rounds and illumination rounds, the Pentagon said. Earlier, officials had said that 120mm mortar rounds and 40mm ammunition for grenade launchers were bought, but later corrected themselves to say that this ammunition was not in this shipment.
The United Nations' top humanitarian official on Thursday made an urgent plea to the U.N. Security Council for a pause in the fighting for humanitarian reasons.
There is a need for Israel and Hamas to comply with humanitarian and human rights law, said Valerie Amos, under-secretary for humanitarian affairs.