Israel on Thursday said it was massing troops along the Gaza border with Palestine and calling up 9,000 reservists ahead of a possible invasion, as the nations plunged closer to all-out war. Egyptian mediators rushed to Israel for cease-fire efforts, to little effect.

JERUSALEM • Israel on Thursday said it was massing troops along the Gaza frontier and calling up 9,000 reservists ahead of a possible ground invasion of the Hamas-ruled territory, as the two bitter enemies plunged closer to allout war. Egyptian mediators rushed to Israel for cease-fire efforts but showed no signs of progress.

The stepped-up fighting came as communal violence in Israel erupted for a fourth night, with Jewish and Arab mobs clashing in the flashpoint town of Lod. The fighting took place despite a bolstered police presence ordered by the nation’s leaders.

The four-day burst of violence has pushed Israel into uncharted territory — dealing with the most intense fighting it has ever had with Hamas while simultaneously coping with the worst Jewish-Arab violence inside Israel in decades. A late-night barrage of rocket fire from Lebanon that landed in the sea threatened to open a new front along Israel’s northern border.

Early Friday, the Israeli military said air and ground troops struck Gaza in what appeared to be the heaviest attacks yet. Masses of red flames illuminated the skies as the deafening blasts from the outskirts of Gaza City jolted people awake. The strikes were so strong that people inside the city, several kilometers away, could be heard screaming in fear.

“I said we would extract a very heavy price from Hamas,” Prime Minister Benjamin Netanyahu said in a videotaped statement. “We are doing that, and we will continue to do that with heavy force.”

The fighting broke out late Monday when Hamas, claiming to be the defender of Jerusalem, fired a barrage of long-range rockets toward the city in response to what it said were Israeli provocations. Israel quickly responded with a series of airstrikes.

Since then, Israel has attacked hundreds of targets in Gaza. The strikes set off scores of earth-shaking explosions across the densely populated territory. Gaza militants have fired nearly 2,000 rockets into Israel, bringing life in the southern part of the country to a standstill. Several barrages targeted the seaside metropolis of Tel Aviv, some 45 miles away.

Gaza’s Health Ministry said the death toll has climbed to 109 Palestinians, including 28 children and 15 women, with 621 people wounded. The Hamas and Islamic Jihad militant groups have confirmed 20 deaths in their ranks, though Israel says that number is much higher. Seven people have been killed in Israel, including a 6-year-old boy.

In Washington, President Joe Biden said he spoke with Netanyahu about calming the fighting but also backed the Israeli leader by saying “there has not been a significant overreaction.”

He said the goal now is to “get to a point where there is a significant reduction in attacks, particularly rocket attacks that are indiscriminately fired into population centers.” He called the effort a “a work in progress.”

Thursday’s visit by Egyptian officials marked an important step in the ceasefire efforts.

Egypt often serves as a mediator between Israel and Hamas, and it has been a key player in ending past rounds of fighting. The officials met first with Hamas leaders in Gaza before holding talks with Israelis in Tel Aviv, two Egyptian intelligence officials said. They spoke on condition of anonymity because they were not authorized to talk to the media. Hamas’ exiled leader, Ismail Haniyeh, was also in touch with the Egyptians, the group said.

Despite those efforts, the fighting only intensified. Israeli aircraft pummeled targets in Gaza throughout the day. And late Thursday, Israel fired tank and artillery shells across the border for the first time, sending scores of terrified residents fleeing for safety.

The airstrikes have destroyed scores of buildings, including three high rises. Israel says the buildings housed Hamas militants or facilities, but civilians were inside as well.

In the northern Gaza Strip, Rafat Tanani, his pregnant wife and four children were killed after an Israeli warplane reduced the building to rubble, residents said.

Sadallah Tanani, a relative, said the family was “wiped out from the population register” without warning. “It was a massacre. My feelings are indescribable,” he said.

Israel has come under heavy international criticism for civilian casualties in Gaza fighting. It says Hamas is responsible for endangering civilians by hiding and launching rockets from civilian areas.

Late Thursday, Israel’s Defense Minister Benny Gantz ordered the mobilization of an additional 9,000 reservists.

The chief military spokesman, Brig. Gen. Hidai Zilberman, said troops were massing along the Gaza border for a possible ground operation. He said tanks, armored vehicles and artillery were being prepared “for mobilization at any given moment.”

Hamas showed no signs of backing down. It launched several intense barrages of rockets throughout the day and fired its most powerful rocket, the Ayyash, 120 miles into southern Israel. The rocket landed in the open desert but briefly disrupted flight traffic at the southern Ramon airport. Hamas also launched a drone that Israel said it quickly shot down.