"Three IDF soldiers were killed Wednesday night in combat while uncovering an offensive tunnel shaft in south Gaza," Xinhua quoted the spokesperson as saying.
"The tunnel were booby-trapped with two explosive devices that detonated when the soldiers entered."
The Israeli Air Force has struck about 40 targets in Gaza since Wednesday morning, including militants operating in underground tunnels and several who fired anti-tank missiles at Israeli soldiers, the spokesperson said.
On Wednesday evening, Palestinian sources in Gaza reported that 17 people were killed and more than 160 injured in an artillery attack on the Shujayieh market in Gaza city.
The Israeli security cabinet convened for nearly five hours Wednesday to discuss the operation's progress and international attempts to reach a cease-fire agreement, which have thus far produced no results.
Earlier, the Israeli military announced a four-hour humanitarian truce in areas where the Israeli soldiers are not currently operating.
The territories where the IDF is operating include Beit Hanun in the northern Gaza Strip, Shujayieh in east Gaza city and Rafah in the south.
But Hamas said it was not involved in any humanitarian cease-fire discussions and that the IDF announced it unilaterally "for media purposes".
Several rocket barrages were launched shortly after the truce came into effect at 3 p.m., as the Israeli Air Force continued to pound the strip.
According to the Palestinian health ministry, at least 1,327 Palestinians have been killed and more than 7,200 injured, mostly civilians, since Israel's strike began on July 8.
Fifty-six Israeli soldiers have died since Israel's ground incursion into the Gaza Strip commenced July 17, and about 120 soldiers injured.