Hamas said its leader in Lebanon, Fateh Sherif Abu el-Amin was killed, along with his wife, son, and daughter in a strike that targeted their house in a Palestinian refugee camp in the southern city of Tyre early on Monday.
As Israel escalates hostilities against Iran's allies in the region, the Popular Front for the Liberation of Palestine (PFLP) said three of its leaders were killed in a strike that targeted Beirut's Kola district.
The strike hit the upper floor of an apartment building, Reuters witnesses said.
There was no immediate comment from Israel's military.
Many of Israel's attacks have been carried out in the south of Lebanon or Beirut's southern suburbs. (AP PHOTO)
Israel's increasing frequency of attacks against the Hezbollah militia in Lebanon and the Houthi militia in Yemen have prompted fears that Middle East fighting could spin out of control and draw in Iran and the United States, Israel's main ally.
The PFLP is another militant group taking part in the fight against Israel.
Israel on Sunday launched air strikes against the Houthi militia in Yemen and dozens of Hezbollah targets throughout Lebanon after earlier killing the Hezbollah leader.
The Houthi-run health ministry said at least four people were killed and 29 wounded in air strikes on Yemen's port of Hodeidah, which Israel said were a response to Houthi missile attacks.
In Lebanon, authorities said at least 105 people had been killed by Israeli air strikes on Sunday.
Lebanon's health ministry has said more than 1000 Lebanese have been killed and 6000 wounded in the past two weeks, without saying how many were civilians.
The escalation has put Beirut on edge, with Lebanese fearful that Israel will expand its military campaign.
"There is nothing else to say or add, except God save Lebanon," Beirut resident Nawel said.
"What will happen to me is the same as what can happen to anyone."
The government said a million people - a fifth of the population - have fled their homes.
At least four people were killed in Israeli air strikes on Yemen's port of Hodeidah. (AP PHOTO)
The intensifying Israeli bombardment over two weeks has killed a string of top Hezbollah officials, including its leader Sayyed Hassan Nasrallah.
Israel has vowed to keep up the assault and says it wants to make its northern areas secure again for residents who have been forced to flee Hezbollah rocket attacks.
Israeli drones hovered over Beirut for much of Sunday, with the loud blasts of new air strikes echoing around the Lebanese capital.
Displaced families spent the night on benches at Zaitunay Bay, a string of restaurants and cafes on Beirut's waterfront.
Many of Israel's attacks have been carried out in the south of Lebanon, where the Iran-backed Hezbollah has most of its operations, or Beirut's southern suburbs.
Monday's attack in the Kola district appeared to be the first strike within Beirut's city limits.
Syrians living in southern Lebanon who had fled Israeli bombardment had been sleeping under a bridge in the neighbourhood for days, residents of the area said.
The United States has urged a diplomatic resolution to the conflict in Lebanon but has also authorised its military to reinforce in the region.
US President Joe Biden, asked if an all-out war in the Middle East could be avoided, said: "It has to be."
He said he would be talking to Israeli Prime Minister Benjamin Netanyahu.
