GAZA, Dec 3 (Reuters) - The Israeli military said its ground forces were active across the Gaza Strip as Israeli forces bombed swathes of the besieged enclave on Sunday (Dec 3), killing and wounding dozens of Palestinians, as civilians sought shelter in a shrinking area of the south.

The militant group Hamas said its fighters clashed with Israeli troops about 2km from the southern city of Khan Younis. Residents, many of whom had moved there to flee earlier attacks in the conflict, said they could hear tank fire and feared a new Israeli ground offensive was building.

The Israeli military earlier ordered people to evacuate some areas in and near the city, but made no announcement of any new southern ground assault.

"The IDF (Israel Defence Forces) continues to extend its ground operation against Hamas centres in all of the Gaza Strip," spokesperson Rear Admiral Daniel Hagari told reporters in Tel Aviv in the clearest sign its planned ground offensive in the south had begun. "The forces are coming face-to-face with terrorists and killing them."

Fuelling fears the conflict could spread to destabilise the region, Yemen's Iran-allied Houthi movement said it attacked two Israeli ships in the Red Sea with an armed drone and a missile on Sunday, in a move to stand with the Palestinians.

The Pentagon also said it was aware of reports of an attack on an American warship, the USS Carney, without going into detail.

An Israeli military spokesman Rear Admiral Daniel Hagari said the two ships had no connection to Israel.

The Jabalia refugee camp in the north of Hamas-ruled Gaza was among the sites reported hit from the air. A Gazan health ministry spokesperson said several people were killed by an Israeli air strike.

Footage obtained by Reuters showed a boy covered in grey dust, sitting weeping amid crumbled cement and rubble from collapsed buildings.

"My father was martyred," he cried in a hoarse voice. A girl in a pink sweatshirt, also coated with dust, stood between piles of rubble.

Bombardments from war planes and artillery were also concentrated on Khan Younis and Rafah, another city in Gaza's south, residents said, and hospitals were struggling to cope with the flow of wounded.

Israel's government spokesperson, Eylon Levy, said the military had struck more than 400 targets over the weekend "including extensive aerial attacks in the Khan Younis area" and had also killed Hamas militants and destroyed their infrastructure in Beit Lahiya in the north.

There was no immediate comment on the reports of specific attacks.

The renewed warfare followed the end on Friday of a seven-day pause in the fighting between Israeli forces and Hamas militants which had allowed an exchange of 105 hostages held by Hamas, most of them Israelis, for 240 Palestinian prisoners.

The latest violence took place despite calls from the United States, Israel's closest ally, for Israel to limit harm to Palestinian civilians in the new phase of its offensive, focused on the south.

More than 15,523 people have been killed, according to Gaza's health ministry, in nearly two months of warfare that broke out after a Hamas cross-border raid on southern Israel on Oct 7 in which 1,200 Israelis were killed and around 240 taken hostage. Israel says Hamas continues to hold 136 hostages.

Israel has vowed to annihilate Hamas. The Iranian-backed group is sworn to Israel's destruction. The initial Hamas attack and the ensuing war amount to the bloodiest episode in the decades-old wider Israel-Palestinian conflict.

Photo from Reuters