BEIRUT, Aug 1 (Reuters) - At least three people were killed on Sunday in an ambush on Shi"ite mourners in a town south of Beirut, a day after a revenge killing of a member of Lebanon"s Hezbollah group, security sources and a senior source in the group said. The three were shot in the town of Khaldeh, where sectarian tensions have long flared between the town"s mixed Shi"ite and Sunni residents. Several others were taken to hospital in civilian cars, witnesses said. Footage of a video broadcast on Hezbollah"s Manar TV channel showed a volley of gunfire being fired on the convoy of mourners arriving at the home of the slain member of Shi"ite group Hezbollah. Politicians voiced concern as the incident unfolded that any escalation could compound an array of crises in Lebanon given its political vacuum. President Michel Aoun said the situation "does not allow any security incidents" that could inflame sectarian tensions. Iranian-backed Hezbollah, Lebanon"s most powerful armed group, in a statement urged the authorities to pursue the culprits saying the incident reflected lawlessness and bigotry. In a later statement, Hezbollah said two of the mourners were confirmed dead in what it said was a planned ambush and called on the army and security forces to restore security. Sunni Arab tribes who reside in the town said in a statement after the slaying of Hezbollah member Ali Shibli on Saturday, during a wedding, that they had taken revenge for the death of one of their relatives during earlier sectarian clashes in the same area. A grouping of Arab Sunni tribes in Lebanon also issued a statement saying they did not want to be drawn into an armed confrontation but blamed Hezbollah for the troubles and accused it of stirring sectarian tensions. Prime Minister designate Najib Mekati called on the head of the army to increase its security presence in the town, which lies on a coastal highway leading to the south of the country. Local television networks showed footage of armed youths rampaging in the area. The army, which sent reinforcements to Khaldeh, said it would shoot at any source of gunfire.