Gunmen killed three Lebanese Shiites and a Turk in Lebanon's Bekaa Valley, a security source said, revising an earlier toll breakdown, as the conflict in neighbouring Syria raised fresh tensions.
The unidentified assailants shot dead "two members of the Jaafar family, an Amhaz family member and a Turk" in an ambush while they were smuggling fuel through the Qaa area, he told AFP, asking not to be named.
He had initially identified the victims as four Lebanese and said a fifth man was seriously wounded.
But he revised the account to identify the fourth man killed as a Turk with a Lebanese mother, a resident of eastern Lebanon's Bekaa Valley.
The incident occurred in an agricultural part of Qaa, home to a predominantly Sunni population.
The two Shiite families Jaafar and Amhaz are among the most influential in the Bekaa region.
Tensions were running high in the wake of the incident, the source said, with armed members of the Jaafar family gathering around five kilometres (three miles) from the mainly Sunni town of Arsal.
Sunni residents of the area, in a statement received by AFP, condemned "this attack on honourable members of the region... that aims to sow sectarian discord".
"We disassociate ourselves from the perpetrators of this massacre whatever their identity," they said, urging the authorities to hunt down the assailants.
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People in the Baalbek and Hermel region, from where the three Lebanese victims come from, also issued a statement stressing the importance of keeping the peace between the communities.
Hezbollah's Al-Manar television picked up their call for restraint. The station also called for local people not to react to the incident, denouncing what it described as an "attempt to draw the people of the region into internal conflicts."
It said the crime was one of a series committed by "mercenaries who are working to sow dissension in the region".
An army statement said it had increased patrols in the area and called for calm, saying it would "allow no one to exploit this unfortunate incident and threaten national unity".
The conflict in Syria, pitting a Sunni-led opposition against a regime dominated by Alawites, an offshoot of Shiite Islam, has worsened tensions in Lebanon.
The powerful Lebanese Shiite movement Hezbollah backs the regime of President Bashar al-Assad and has sent fighters to battle alongside Syria's army.
Lebanon's Sunni-led opposition, however, backs the uprising against Assad.
The fighting has regularly spilled over into Lebanon, with rockets fired from Syria landing in Sunni and Shiite areas along the border. The Syrian air force has also launched raids inside Lebanese territory.
Hezbollah commands support throughout much of eastern Lebanon along the frontier, but Sunni areas such as Arsal within the region back the Syrian uprising.