Israel's air force carried out intense airstrikes on mountains overlooking a southern city in Lebanon on Friday (local time), in an attack that the Israeli military said targeted underground assets of the Hezbollah militant group.

Shortly afterwards, an apartment building in the nearby city of Nabatieh was struck, killing one woman, wounding 11 and knocking out the building's top floor, according to Lebanon's state news agency.

The state-run National News Agency reported that the woman killed lived in Germany and had come back to Lebanon less than a month earlier to visit family.

It wasn't immediately clear if she was a German citizen. The woman's apartment was hit by an Israeli drone strike, according to the report.

The Israeli army, in a statement posted on X, denied targeting a civilian building.

The statement said the building was hit by a Hezbollah rocket that had been stored at another location that was targeted by an airstrike and "launched, and exploded as a result."

It blamed Hezbollah for storing weapons near residential areas.

Since the 14-month Israel-Hezbollah war ended with a US-brokered ceasefire in November, Israel has carried out almost daily airstrikes on southern Lebanon.

Friday's strikes were more intense than usual.

"We are steadfast no matter how much you bomb us with your fighter jets and drones," Hassan Ghandour, a Shiite cleric from Nabatieh, told The Associated Press at the scene of the building.

Lebanon's president and prime minister condemned the Israeli strikes on south Lebanon, saying they violated the ceasefire deal.

The airstrikes on the mountains overlooking Nabatieh came in two waves, and bunker busters were used, Lebanon's state-run National News Agency reported.

NNA said that four people were slightly wounded in the airstrikes outside the city.

The Israeli military said in a statement that its fighter jets struck a site used by Hezbollah to manage its fire and defence array in the area and is part of a significant underground project that was completely taken out of use.

The Israeli army said that it identified rehabilitation attempts by Hezbollah beforehand and struck infrastructure sites in the area.

There was no immediate comment from Hezbollah.

Hezbollah suffered significant losses on the battlefield during the war, which left more than 4000 people dead in Lebanon and caused destruction amounting to $11 billion. In Israel, 127 people died, including 80 soldiers.

As part of the ceasefire deal, Hezbollah was pushed away from areas bordering Israel in south Lebanon and isn't allowed to have an armed presence south of the Litani River.

Friday's airstrikes were north of the river.