Most of the casualties in Sunday's violence came in the Shijaiyah neighborhood, located between Gaza City and the Israeli border.

On Sunday alone, Israel said that 13 soldiers had been killed in the latest fighting, and Gaza health officials put the Palestinian death toll at more than 100.

425 Palestinians and 18 Israeli soldiers have died in Israel's 13-day-long offensive. Two Israeli civilians also died in mortar and rocket attacks.

The current conflict between Israel and Hamas began on July 8, with Israel announcing on July 17 that it would undertake ground operations in Gaza.

During a news conference at Israel's security headquarters in Tel Aviv, Israeli Prime Minister Benjamin Netanyahu and Defense Minister Moshe Yaalon expressed regret for civilian deaths, but placed full responsibility on Hamas.

"We are not deterred. We will continue with this operation as long as is necessary," Netanyahu said.

Palestinian President Mahmoud Abbas declared three days of mourning over the "brutal Israeli aggression" in Shijaiyah and demanded international intervention.

Hamas claims Israeli soldier 'kidnapped'

The armed wing of the Palestinian Hamas group claimed on Sunday night that it had kidnapped an Israeli soldier.

In a televised address, Hamas spokesman Sami Abu Zuhri said, "The announcement by the Qassam Brigades of the capture of a Zionist soldier is a great victory and revenge for the blood of the martyrs."

The Qassam Brigades claimed the soldier had been kidnapped 24 hours earlier during an ambush on Israeli forces in the Tuffah district on the eastern edges of Gaza City.

An Israeli military spokeswoman in Tel Aviv said they were investigating the claim.

International push for a truce

US President Barack Obama told Israeli Prime Minister Benjamin Netanyahu he was concerned about the rising number of civilian deaths and said US Secretary of State John Kerry would head to Cairo on Monday to join efforts for a truce.

UN Secretary General Ban Ki-moon was also due to meet Egyptian President Abdel Fatah al-Sisi in Cairo to discuss proposals for a ceasefire.

During a visit to Doha on Sunday, he urged Israel to "exercise maximum restraint" and spare civilian lives in its campaign in the Gaza Strip.

Palestinian President Mahmoud Abbas was scheduled to meet with Ban in Qatar's capital at the start of the UN chief's trip to the Middle East to help broker a ceasefire.

Diplomatic sources said the UN Security Council in New York would hold an emergency meeting on Sunday night at Jordan's request.

lw/av (AFP, AP, Reuters, dpa)