(AFP) - World leaders urged Israel against a full scale invasion of Lebanon after it's army said it began limited ground operations in the latest step in its showdown with Hezbollah.

The two arch-foes have engaged in low-level clashes since the outbreak of war in Gaza, but tensions have skyrocketed in recent weeks as Israel shifted its focus to its northern border and staged a strike in which Hezbollah chief Hassan Nasrallah was killed.

- Avoid 'greater suffering': UN -

After Israel said its troops were engaged in "limited raids" in Lebanon, the United Nations warned against those raids turning into a "large-scale ground invasion".

"The consequences for civilians have already been terrible," Liz Throssell, spokeswoman for the UN rights office, told reporters in Geneva.

"We fear a large-scale ground invasion by Israel into Lebanon would only result in greater suffering."

While warning that Israel entering Lebanon would be "in violation of Lebanese sovereignty and territorial integrity", the UN peacekeeping force in south Lebanon told AFP there was "no ground incursion right now".

- Limited backing: US -

US President Joe Biden indicated Monday he was opposed to Israel putting troops on the ground in Lebanon, adding: "We should have a ceasefire now".

But late on Monday Defense Secretary Lloyd Austin gave Washington's backing to Israel "dismantling attack infrastructure along the border".

- No troops for Hezbollah: Iran -

Though Hezbollah's key backer Iran had vowed Israel's "destruction" for the killing of the millitant group's chief Nasrallah, it said ahead of the Israeli action that it would not deploy troops to Lebanon.

"There is no need to send extra or volunteer forces of the Islamic Republic of Iran," said foreign ministry spokesman Nasser Kanani.

The same applied to Gaza, where Israel has been locked in war with Hamas -- also backed by Tehran -- since the Palestinian militant group's October 7 attack on Israel that began the war.

- Immediate Israeli withdrawal: Russia -

Russia, which has close ties with Iran, urged Israel "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".

"We express our solidarity with the leadership and people of friendly Lebanon, which has been subjected to armed aggression," the Russian foreign ministry said.

- 'Highly concerned': China -

In the wake of the Israeli announcement, China said it was "highly concerned about the escalation" and was opposed to "infringements on Lebanon's sovereignty, security, and territorial integrity".

A foreign ministry statement also warned against "any actions that exacerbate conflicts and lead to a further escalation of the regional situation."

- 'Unlawful invasion attempt': Turkey -

A frequent critic of Israel's strikes on Lebanon and conduct of the war in Gaza, Turkey slammed Israel's ground offensive as an "unlawful invasion attempt".

"This attack must end as soon as possible and Israeli soldiers must withdraw from Lebanese territory," the foreign ministry said. "All state and international organisations, especially the UN, must stop Israel without wasting any more time," said President Recep Tayyip Erdogan, who added that Israel might even target Turkey.

- 'False claims': Hezbollah -

Yet Hezbollah itself denied that Israeli troops had crossed into Lebanon.

"All the Zionist claims that (Israeli) occupation forces have entered Lebanon are false claims," a Hezbollah spokesman told the, adding there had "not yet been any direct ground clash between (Hezbollah) resistance fighters and (Israeli) occupation forces".

A source from the Lebanese army -- whose capabilities are dwarfed by Hezbollah's military might -- likewise said that it "had not observed any penetration by Israeli enemy forces into Lebanese territory".

© Agence France-Presse