Seventy Palestinians were killed Sunday in a heavy bombardment of a Gaza neighborhood and 13 Israeli soldiers were slain in the most intense day of fighting in Israel’s current offensive against Hamas fighters, officials said. The Hamas military also announced that its fighters had captured an Israeli soldier.

Abu Obaida, a spokesman for the Al Qassam Brigades, appeared on Hamas TV to announce the soldier had been taken prisoner. Minutes later, there were fireworks and shouts of “God is great!” from loud speakers.

An Israeli military spokeswoman said the army was investigating the claim.

A kidnapped Israeli soldier would represent a victory for Hamas and a difficult new challenge for Prime Minister Benjamin Netanyahu.

The last Israeli soldier abducted by Hamas was Gilad Shalit, who spent more than five years in captivity before being released in a controversial prisoner exchange in 2011 that freed 1,027 Palestinian security prisoners, some of whom carried out terror attacks against Israeli civilians. Shalit was captured by Hamas operatives who tunneled into Israel and snatched the corporal.

Seventy Palestinians were killed Sunday in a heavy bombardment of a Gaza neighborhood and 13 Israeli soldiers were slain in clashes in the most intense day of fighting in Israel’s ongoing offensive against Hamas fighters, officials said.

The reported seizure of the Israeli soldier capped the most violent day of the nearly two-week-old offensive. So far, 18 Israeli soldiers have been killed since the armed forces launched a ground operation Thursday after days of airstrikes on the coastal strip, the Israeli military said. The Israeli death toll is now higher than during the Israeli military’s 2009 incursion into Gaza, when 13 Israelis were killed.

Israel pummeled a neighborhood in east Gaza overnight Sunday, producing gruesome images of bodies in the streets amid masses of rubble. The Gaza Health Ministry said 70 Palestinians were killed in the fighting in Shijaiyah. All told, almost 100 Gaza residents have died in 24 hours, the highest daily total.

There are also more than 81,000 displaced people seeking refuge in 61 shelters run by the United Nations.

Secretary of State John F. Kerry is planning to travel to Cairo soon to seek “an immediate cessation of hostilities” in the conflict, the White House said in a statement. It said that President Obama spoke with Netanyahu on Sunday, reaffirming Israel’s right to defend itself but raising “serious concerns” about the growing number of casualties in the fighting.

Thousands of panicked residents were pouring out of Shijaiyah in mass flight Sunday morning. The scene at Shifa Medical Center, Gaza’s main hospital, was chaotic. Ambulance drivers reported great difficulty entering the district, which bore the brunt of continuous fire.

After a brief lull at dawn, there was an increase of artillery and tank shelling at midmorning on Sunday. Explosions sounded closer to the center of Gaza City, and the sky was filled with Israeli drones witnessing the exodus of civilians.

Residents said land and naval bombardment around Shijaiyah was the heaviest in the 13 days of fighting, but there was also intense firing east of Khan Younis and in the far south by Rafah.