Beirut, Lebanon (CNN) -- A senior Hezbollah commander was killed outside his home in Beirut early Wednesday, a Lebanese security official told CNN.
Hassan Hawlo Lakkis was shot four times, "in the head and in the shoulder," the source said.
The source added that a silenced pistol was probably used and there were "maybe" two or three attackers.
Hezbollah said in a statement Lakkis was "assassinated" in the southern district of Hadath as he was returning home from work.
The militant Shiite group blamed Israel for the killing -- but Israel denied it.
'"This is strictly nothing to do with Israel," Yigal Palmor, spokesman for the Israeli Foreign Ministry said.
Hezbollah said Lakkis had been a member of the group since its formation.
He is described as the group's chief procurement officer in the book "Hezbollah: The Global Footprint of Lebanon's Party of God" by Matthew Levitt of The Washington Institute.
Later Wednesday, a little known Sunni group claimed responsibility on Twitter for the assassination.
"The Free Sunni Baalbeck Brigade officially claims responsibility for the heroic jihadi operation to assassinate the commander in the Party of Satan Hassan Hulu Al-Laqees in the heart of their home," the tweet posted Wednesday read.
The term "Party of Satan" is a play on Hezbollah that, in Arabic, translates to "Party of God."
In another tweet, the Baalbeck Brigade said the killing was "only the beginning of a great purification battle."
It accused Hezbollah of harassing and arresting Sunnis.
CNN could not independently verifying the authenticity of this claim
CNN's Nick Paton Walsh reported from Beirut, Lebanon; Marie-Louise Gumuchian wrote from London