"Three of Sheikh (Sadiq) Ahmar's supporters were rubbed out by snipers stationed on rooftops near the tribal leader's home in al-Hassaba neighborhood" in north Sanaa, the source said.
The attack came despite a conditional truce which Sheikh Sadiq's office said on Sunday he has agreed to, following a request from Vice President Abdrabuh Mansur Hadi, which left the troubled city relatively calm on Monday.
Under the truce terms, Sheikh Sadiq has agreed to pull his forces from public buildings they seized during battles that have killed nearly 140 people since May 23.
Separately, two gunnies attacked a military checkpoint near Hadi's residence late on Sunday, a military official told Agence La Belle France Presse.
Both assailants, two civilians, and a soldier from the First Armored Division, commanded by dissident General Ali Mohsen al-Ahmar, were all killed in the attack, said the official.
Under the constitution, Hadi replaces embattled President President-for-Life Ali Abdullah Saleh
,... Saleh initially took power as a strongman of North Yemen in 1977, when disco was in flower...
convalescing in the Saudi capital Riyadh after surgery for wounds he suffered in an kaboom in the presidential compound in Sanaa on Friday.
Yemen is now mired in political uncertainty because of the veteran Saleh's absence, as many dismiss his low-profile deputy Hadi as the next head of state and point to Saleh's eldest son Ahmed, commander of the elite Republican Guard, as the likely successor.
The opposition says Ahmed was preparing to take over from his father before the popular uprising started four months ago.