Israeli forces are making their deepest incursion inside Lebanon since they withdrew from the country over a quarter-century ago, despite a nominal U.S.-brokered ceasefire and the first direct talks between the countries in decades.

The Israeli advance presents a challenge in the emerging deal to extend the Iran war ceasefire as Tehran wants any agreement to end fighting in Lebanon, too. Qatar called it a "dangerous escalation." Germany's foreign minister said it was cause for serious concern, according to German press agency dpa. There was no comment by the United States.

Israeli troops have captured a strategic mountain topped with a Crusader-built castle in southern Lebanon in the deepest incursion into the country in more than a quarter-century, the military said Sunday, while U.S. Secretary of State spoke to Lebanese and Israeli leaders in an effort to keep negotiations going.

U.S. Secretary of State Marco Rubio spoke to Lebanese President Joseph Aoun and Israeli Prime Minister Benjamin Netanyahu to propose a fresh path to continue ongoing negotiations, according to a U.S. official who spoke on condition of anonymity to discuss private diplomatic conversations. Under the proposal, Hezbollah would halt all attacks on Israel and Israel would refrain from escalating military operations in the Lebanese capital of Beirut, according to the official.

Israel's government ordered strikes on the southern suburbs of Beirut on Monday, a day after its ground forces reached their deepest point in Lebanon in 26 years and as Hezbollah fired rockets at northern Israel including the outskirts of coastal city of Haifa.

A joint statement by Israeli Prime Minister Benjamin Netanyahu and Defense Minister Israel Katz said that following what they called repeated violations of the ceasefire by Hezbollah and the "attacks against our cities and citizens," they have ordered the Israeli military to attack targets in Beirut's southern suburbs known in Arabic as Dahieh.

Israeli Prime Minister Benjamin Netanyahu on Sunday said he ordered the Israeli army to deepen its deployment in Hezbollah strongholds north of the Litani River, noting that "soon Hezbollah will no longer have the ability to threaten northern Israel."

Israel's flag flew over the medieval fortress on Beaufort in Lebanon on Sunday as it warned Lebanese civilians to evacuate a large area of the south of the country ahead of stepped up ground operations.

Shelling was audible and smoke rose from the surrounding area as the invading army's banner was seen by AFP above the castle, which Israeli forces famously used as a base during their previous two-decade long occupation.

The Trump administration has extended protections shielding about 11,000 Lebanese from deportation, allowing them to stay and work in the United States for another six months.

The decision, announced Thursday by the Department of Homeland Security, marked a rare reprieve for people protected by temporary measures which have been harshly criticized by Republicans. The extension comes amid ongoing fighting in southern Lebanon between Israeli troops and Hezbollah fighters.

Hezbollah has again rejected direct talks between Lebanon and Israel on the eve of military negotiations between the two sides.

Israel's air force carried out an airstrike on the Choueifat area on the edge of Beirut's southern suburbs on Thursday afternoon, the Israeli military said, further straining a fragile ceasefire a day ahead of crucial negotiations in Washington.

The strike hit an apartment building. Videos from Choueifat, close to Beirut's international airport, showed white smoke billowing from a residential neighborhood.

Five people were killed and 21 others wounded overnight when an Israeli drone struck an apartment building in the southern city of Sidon where some displaced families lived, the first such attack on Sidon during the latest escalation.

The attack likely came in response to a drone attack that killed a female Israeli soldier in north Israel. LBCI television had reported that Israel had informed the U.S. of its intention for escalation after the attack.

Since a ceasefire was reached in April, the Lebanese capital of Beirut has been spared from strikes, except for one strike on its suburbs.

But Israel's latest moves have caused fear, urging residents of Dahieh to evacuate once again, after Israeli Prime Minister Benjamin Netanyahu said that he had authorized more intensive strikes targeting Hezbollah across Lebanon.