There is uncertainty around the statement as the exact position of the troops and the nature of the attack remains unclear.

Israeli media are reporting that residents within four kilometres of the border have been ordered into bomb shelters.

The development comes after Israel earlier said it was massing troops along the Gaza frontier and calling up 9,000 reservists as days of cross-border fighting showed no sign of abating.

Just after midnight (local time), Israel Defense Forces tweeted: "IDF air and ground troops are currently attacking in the Gaza Strip."

It was not immediately clear how many troops the tweet was referring to, where they entered or what their objective was.

"I have tried to confirm with the IDF what this means however they haven't provided any more information other than what is in that Tweet," said ABC Middle East correspondent Tom Joyner.

"We have spoken to people in the Gaza Strip, particularly in the northern part of the strip and there don't seem to have been any sightings in the last hour of Israeli troops.

"Certainly from this single tweet, it seems that some kind of escalation is underway."

At least 103 people have been killed in Gaza, including 27 children, over the past four days, Palestinian medical officials said.

Seven people have been killed in Israel: a soldier patrolling the Gaza border, five Israeli civilians, including two children, and an Indian worker, Israeli authorities said.

Israeli Prime Minister Benjamin Netanyahu said the campaign "will take more time" and Egyptian mediators rushed to Israel for ceasefire efforts but showed no signs of progress.

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.

Violence has also spread to mixed communities of Jews and Arabs in Israel, a new front in the long conflict. Synagogues were attacked and fighting broke out on the streets of some towns, prompting Israel's president to warn of civil war.

Worried that the region's worst hostilities in years could spiral out of control, the United States is sending an envoy, Hady Amr. Truce efforts by Egypt, Qatar and the United Nations have so far offered no sign of progress.

US President Joe Biden on Thursday called for a de-escalation of the violence, saying he wanted to see a significant reduction in rocket attacks.

Militants fired rocket salvoes at Tel Aviv and surrounding towns, Israel's commercial heartland, with the Iron Dome anti-missile system intercepting many of them.

Communities near the Gaza border and the southern desert city of Beersheba were also targeted.

Mr Netanyahu said Israel had struck a total of close to 1,000 militant targets in the Gaza Strip.

Israeli aircraft also attacked a Hamas intelligence headquarters and four apartments belonging to senior commanders from the group, the military said, adding that the homes were used for planning and directing strikes on Israel.

Hospitals in Gaza already under heavy pressure because of the COVID-19 pandemic have faced further strain.

Standing beside a Gaza road damaged in Israeli air strikes, Assad Karam, 20, a construction worker, said: "We are facing Israel and COVID-19. We are in between two enemies."

In Tel Aviv, Yishai Levy, an Israeli singer, pointed at shrapnel that came down on a sidewalk outside his home.

"I want to tell Israeli soldiers and the government, don't stop until you finish the job," he said on YNet television.

Israel launched its offensive after Hamas fired rockets at Jerusalem and Tel Aviv in retaliation for Israeli police clashes with Palestinians near al-Aqsa mosque in East Jerusalem during the Muslim fasting month of Ramadan.

A number of foreign carriers have cancelled flights to Israel because of the unrest.

Brigadier-General Hidai Zilberman, the Israeli military's chief spokesman, said attacks on militants' rocket production and launching sites were "disrupting Hamas' activities", but still not to the point of stopping the barrages.

"It is more difficult for them, but we have to say in fairness that Hamas is an organised group, one that has the capability to continue to fire for several more days at the places it has been targeting in Israel," he said on Israeli Channel 12 TV.

He said between 80 and 90 militants had been killed in Israeli attacks.

Hamas armed wing spokesman Abu Ubaida responded to the Israeli troop buildup with defiance, urging Palestinians to rise up.

"Mass up as you wish, from the sea, land and sky," he said.

"We have prepared for your kinds of deaths that would make you curse yourselves."

Source | ABC / Wires