The bodyguard of a top Palestinian commander was shot dead at a refugee camp in southern Lebanon on Sunday, the second such attack in four days, a camp official said.

On December 14, a bodyguard for Mohammed Abdel Hamid Issa, the head of Palestinian party Fatah's police force in the the Ain al-Helweh camp was killed by a masked gunman.

Another of Issa's bodyguards, Amer Fustoq, was killed Sunday in an attack that also left three other injured.

"An unknown man fired on Amer Fustoq in a market in the Ain al-Helweh camp and he was seriously injured", said a camp official who requested anonymity.

Fustoq was taken to a hospital in the coastal city of Sidon, but died from his injuries, according to the same source, who added that three others, including a child, were also injured in the attack.

Lebanon's state news agency ANI reported that the attack came amid clashes between Fatah and a minor Sunni Islamist group Jund al-Sham, or "Soldiers of Damascus."

Automatic gunfire could still be heard inside the refugee camp and many families were leaving the scene in vehicles, according to an AFP correspondent.

Ain al-Helweh, the largest Palestinian camp in the country, is home to about 50,000 refugees and is known to harbour extremists and fugitives.

By long-standing convention, the Lebanese army does not enter the country's 12 refugee camps, leaving security inside to the Palestinians themselves.

The United Nations Relief and Works Agency for Palestinian refugees (UNRWA) estimates that some 425,000 Palestinian refugees are living in Lebanon, a country with a population of four million.

Others, however, estimate the number to be closer to 250,000.