Israel carried out an air strike on a Beirut apartment block on Monday, a Lebanese security source said, killing four people in its first such raid on the heart of the city since the outbreak of the Gaza war last year.

Israel has turned its focus from Gaza to Lebanon in recent days, carrying out attacks on Iran's regional allies. Strikes on Hezbollah targets killed the Iran-backed group's leader Hassan Nasrallah on Friday.

Monday's drone attack targeted a "flat belonging to Jamaa Islamiya", a Lebanese Islamist group, the security source said.

The Popular Front for the Liberation of Palestine (PFLP), a secular left-wing group, said three of its members were killed in Monday's strike on Beirut's Kola district.

The group said in a statement that its military security chief Mohammad Abdel-Aal, military commander Imad Odeh, and Abdelrahman Abdel-Aal were killed.

The Israeli military said it had launched fresh strikes on dozens of Hezbollah targets in Lebanon's Bekaa region on Monday.

Israel "will continue to attack powerfully, damage and degrade Hezbollah's military capabilities and infrastructure in Lebanon", the army said in a statement on Telegram.

Television footage showed the partially flattened floor of the building targeted by the strike, in the predominantly Sunni neighbourhood of Kola, near the road linking the capital to Beirut airport.

AFP journalists reported drones flying over the Lebanese capital throughout Sunday.

Israeli attacks have killed hundreds in Lebanon since last Monday, the deadliest day since the country's 1975-1990 civil war.

Lebanon's health ministry reported at least 105 people killed in Israeli strikes on Sunday, with 359 people wounded.

In the last week, Israeli bombardment has killed more than 700 people, including 14 paramedics over two days, the ministry said.

UN refugee chief Filippo Grandi said "well over 200,000 people are displaced inside Lebanon" and more than 50,000 have fled to neighbouring Syria.

Prime Minister Mikati said up to one million people may have been uprooted, in potentially the "largest displacement movement" in Lebanon's history.