A truce agreed during the brief visit by Prime Minister Hisham Qandil quickly dissolved in violence as what Palestinian security sources said was an Israeli air strike hit northern Gaza, killing two.
Israel accused Hamas of violating the agreement but it denied carrying out any strikes.
"We have not attacked in the past two hours, in addition there have been over 60 rocket launches in the same period of time," an army spokesman said, as Hamas militants from the Ezzedine al-Qassam Brigades admitted having fired more than 40 rockets over the border.
Qandil entered the bomb-scarred territory via the Rafah crossing early morning, decrying an Israeli assault on Gaza since Wednesday which has sent tensions soaring across a Middle East already shaken by Arab Spring uprisings and civil war in Syria.
Speaking at Gaza City's Shifa hospital after seeing the bodies of those killed in Friday's reported air strike, Qandil vowed to intensify Cairo's efforts to secure a truce and end Israel's "aggression" in Gaza.
"Egypt will not hesitate to intensify its efforts and make sacrifices to stop this aggression and achieve a lasting truce," he told reporters.
"What I saw today in Gaza, at the hospital, with the martyrs, cannot be met with silence," Qandil said. "This tragedy should not be met with silence and the whole world should take responsibility to stop the aggression."
On Thursday, Washington said it had urged Egypt "to use its influence in the region to help de-escalate the situation," the US State Department said.
As the violence spiralled, Israel geared up for an expansion of the campaign, with the military sending out call-up papers to 16,000 reservists.
Senior cabinet minister Moshe Yaalon also warned that Israel was considering a ground operation in order to stamp out rocket fire.
"We are preparing all the military options, including the possibility that forces will be ready to enter Gaza in the event that the firing doesn't stop," he wrote in a series of postings on his official Twitter account.
An AFP correspondent on the Israeli side of the border reported seeing tanks massed along the frontier, and a steady stream of reserve soldiers arriving for duty in the area.
Egypt's Islamist President Mohamed Morsi -- who hails from the Muslim Brotherhood movement that gave birth to Hamas -- warned on Thursday that Egypt would not accept Israel's "aggression" in the Gaza Strip.
The bloodshed began on Wednesday afternoon when Israel killed top Hamas military chief Ahmed Jaabari, sparking a massive escalation and a furious response from Cairo which promptly recalled its ambassador to the Jewish state.
US deputy State Department spokesman Mark Toner told journalists that Washington hoped the Egyptian prime minister would deliver a message to halt the rocket fire into Israel.
"We ask Egypt to use its influence in the region to help de-escalate the situation," Toner said.
Gaza was shaken by blasts throughout the night as Israeli warplanes carried out relentless sorties, as Palestinian militants fired more rockets into the Jewish state as the bloodshed entered a third day.
The escalating conflict, which has so far killed 20 Palestinians and three Israelis, who died in rocket fire, has drawn expressions of deep concern internationally and sparked anger in the Arab and Muslim world.
On Thursday, a rocket hit the sea just south of Tel Aviv, the farthest distance ever attained by fire from Gaza, in an attack claimed by the armed wing of Islamic Jihad.
Israeli news networks said it was the first time rockets had been fired at Tel Aviv since the 1991 Gulf War, when the city was hit by Iraqi Scud missiles.