The Israeli military on Tuesday warned people to evacuate nearly two dozen Lebanese border communities hours after announcing the start of ground operations against Hezbollah.

The militant group denied Israeli troops had entered Lebanon, and it wasn't immediately clear if Israeli troops had crossed the border. No photos or video footage has yet emerged showing Israeli ground forces inside Lebanon.

An Associated Press reporter saw Israeli troops operating near the border in armoured trucks, with helicopters circling overhead, but could not confirm ground forces had crossed into Lebanon. Neither the Lebanese army nor a UN peacekeeping force known as UNIFIL, which patrols southern Lebanon, have confirmed that Israeli forces entered.

Israel advised people to evacuate to the north of the Awali River, some 60 kilometres from the border and much farther than the Litani River, which marks the northern edge of a UN-declared zone intended to serve as a buffer between Israel and Hezbollah after their 2006 war.

"You must immediately head north of the Awali River to save yourselves, and leave your houses immediately," said the statement posted by the Israeli military's Arabic spokesperson, Avichay Adraee, on X.

UNIFIL said any such cross-border operation would be a "dangerous development" and a violation of Lebanese sovereignty. In its first statement since Israel announced the start of ground operations, Hezbollah spokesperson Mohammed Afif dismissed what he said were "false claims" of an Israeli incursion.

He said Hezbollah, the Iran-backed force, is ready for "direct confrontation with enemy forces that dare to or try to enter Lebanon."

Rear Adm. Daniel Hagari, the Israeli military's top spokesperson, claimed troops were conducting "localized ground raids" on Hezbollah positions in southern Lebanon to ensure Israeli citizens could return to their homes in the north. He did not provide any evidence.

Israeli air defence systems are fully prepared for any attack from Iran, but no threat has been identified at present, Hagari said at a televised briefing, minutes after multiple reports from U.S. media outlets warned that an attack could be imminent, citing sources in the White House.

Israel and its allies are in a high state of readiness, and any attack from Iran would have repercussions, Hagari said.

In April, Iran launched its missiles and drones at Israel in response to an apparent Israeli strike on an Iranian consulate in Syria. According to reports, a number of other countries helped Israel largely repel the Iranian onslaught.

The border region has largely emptied out over the past year as the two sides have traded fire. But the scope of the evacuation warning raised questions about how deep Israel plans to send its forces into Lebanon as it presses ahead with a rapidly escalating campaign against Hezbollah. Prime Minister Benjamin Netanyahu has said that returning thousands of Israelis to their northern border communities as soon as possible is a top priority.

Hezbollah boasts of new weapon

Anticipating more rocket attacks from Hezbollah, the Israeli army announced new restrictions on public gatherings and closed beaches in northern and central parts of the country, including in Tel Aviv and Jerusalem. The military also said it was calling up thousands more reserve soldiers to serve on the northern border.

Hezbollah said it fired salvos of a new kind of medium-range missile, called the Fadi 4, at the headquarters of two Israeli intelligence agencies near Tel Aviv. Afif, the Hezbollah spokesman, said the missile attack "is only the beginning."

Hezbollah began firing rockets into northern Israel shortly after the Hamas-led attack on Israel nearly a year ago ignited the war in Gaza. Israel has launched retaliatory airstrikes, and the conflict has steadily escalated.

In recent weeks, Israel has unleashed a punishing wave of airstrikes across large parts of Lebanon, killing Hezbollah leader Hassan Nasrallah and several of his top commanders, as well as many civilians.

Recent airstrikes wiping out most of Hezbollah's top leadership and the explosions of hundreds of pagers and walkie-talkies belonging to Hezbollah indicate that Israel has infiltrated deep inside the group's upper echelons.

Even after its recent losses, Hezbollah vowed Monday to keep fighting. The group's acting leader, Naim Kassem, said in a televised statement Monday that Hezbollah commanders killed in recent weeks have already been replaced.

More than 1,000 people have been killed in Lebanon in Israeli strikes over the past two weeks, nearly a quarter of them women and children, according to the Health Ministry. Hundreds of thousands of people have fled their homes.

The last time Israel and Hezbollah engaged in ground combat was a monthlong war in 2006.

There was no word on how long the latest operation would last, but the Israeli army said soldiers had been training and preparing for the mission in recent months.

Hezbollah is a well-trained militia, believed to have tens of thousands of fighters and an arsenal of 150,000 rockets and missiles. The last round of fighting in 2006 ended in a stalemate, and both sides have spent the past two decades preparing for their next showdown.

Russia calls on Israel to stop attacks in Lebanon

The crisis has seen a number of countries and international bodies urge for de-escalation, with the Kremlin joining the call on Tuesday.

"Russia strongly condemns the attack on Lebanon and calls on the Israeli authorities to immediately cease hostilities, withdraw their troops from Lebanese territory and engage in a real search for peaceful ways to resolve the Middle East conflict," the Russian foreign ministry said in a statement.

WATCH | What a full-scale invasion might look like:

How might an Israeli ground invasion of Lebanon unfold? | About That

As tensions grow along Israel's northern border with Lebanon, a top Israeli military official says troops are preparing for a potential ground invasion targeting Hezbollah military outposts. Andrew Chang explains what a full-scale invasion would look like and why many world leaders are fearing the worst. Images supplied by Getty Images and Reuters.

Countries and multinational companies are also adapting in the wake of the crisis.

A British government-chartered flight is due to leave Beirut on Wednesday to evacuate U.K. nationals.

A number of airlines have cancelled flights to Tel Aviv "until further notice" or "for the foreseeable future," including Air Canada. On Tuesday, Dutch airline KLM said it would suspend flights until the end of 2024, Dutch news agency ANP reported. Delta in the U.S. had previously announced it was suspending flights at least until 2025.