Israeli forces in the southern Gaza Strip are searching for a missing soldier they fear may have been captured by Palestinian fighters during clashes, the army said.

Friday's statement came as the military announced that the 72-hour agreed-upon ceasefire with Hamas was over just less than six hours after its official start.

"Initial indications suggest that a soldier has been abducted by terrorists," a statement said. "The Israel Defence Forces are currently conducting intelligence efforts and extensive searches in order to locate the missing soldier."

Second Lieutenant Hadar Goldin, 23, of Kfar Saba, was named as the soldier presumed to be captured by Hamas on Friday, according to the the army spokesperson's office.

The United Nations said two soldiers had been reported killed in Rafah, on the border with Egypt, apparently during the same firefight that led to the abduction.

Hamas, the main political and military power in Gaza, neither confirmed nor denied the capture.

But it said Israel's announcement of the capture was simply a "justification for Israel retreating from the truce, and a cover-up for massacres especially in Rafah," referring to Israeli shelling that killed at least 35 people just hours after the truce took hold.

If confirmed, the soldier would be the second to go missing since Israel launched its ground offensive in Gaza.

Lerner said the soldier went missing during a battle with fighters who emerged from a concealed tunnel, one of whom blew himself up with an explosives belt.