IDF soldiers mourn death of Israeli soldier.
Israeli soldiers mourn with the brother of Israeli soldier Bnaya Rubel (kneeling) during Rubel's funeral in Holon, near Tel Aviv July 20, 2014. REUTERS/Nir Elias

Israel Defense Forces announced Sunday evening that 13 soldiers from the elite Golani Brigade have been killed since Saturday night when the IDF escalated its offensive in the Gaza Strip even as reports put the Palestinian death toll at above 500.

Large infantry forces entered Gaza overnight as IDF expanded Operation Protective Edge to destroy tunnels Israel says Hamas uses to launch attacks inside its border. Israeli military sources said Hamas gunmen have increased attacks against IDF soldiers who are reportedly discovering tunnel entrances inside Palestinian homes near the border with Israel. Thirteen cross-border tunnels have been destroyed since Thursday night and the air force struck some 500 targets since the start of the ground operations, according to the military.

IDF has so far released the names of five of the Golani Brigade soldiers killed on Thursday. Two of the 13 soldiers killed were U.S. citizens, the IDF confirmed.

"The IDF is currently completing the identification process; when the process is completed, and with the families' approval, the names of the fatalities will be released," a statement said.

The Golani Brigade, also known as the 1st Brigade, occupies a special place in Israeli history for retaking Mount Hermon in the Golan Heights from Syrian forces during the 1973 Arab-Israeli war.

In the Tufah neighborhood, north of Shuja’iyya, troops from the brigade fell to an ambush when a rocket-propelled grenade was fired at their armored vehicle, killing seven and severely wounding two, Haaretz reported. The attack drew criticism from senior IDF officers for the military's use of armored vehicles built in the 1960s. Six more soldiers from the Golani Brigade were killed in separate gun battles.

This reportedly brings the Israeli military death toll so far to 18. Two Israeli civilians have also been reportedly killed in rocket and mortar attacks that have wounded dozens of soldiers.

More than 500 Palestinians have been killed so far in the near two-week conflict, Agence France-Presse reported.