A Sunni Islamist group took credit on Thursday for the car bombing in a Hezbollah stronghold in Beirut which killed at least 20 people.

Shortly after news of the attack broke, an online video surfaced showing three masked men, two of them holding rifles, in front of a white flag inscribed with the Islamic profession of faith, reported AFP.

"You, the pig Hassan Nasrallah, we send you our second powerful message because you haven't understood yet," said one member of the group, which called itself the Company of Aisha Umm al-Muminin, the Prophet Mohammed's favorite wife.

Arab affairs expert Dalit Halevi said that the group also accused the Hezbollah chief of being “an agent of Iran and Israel."

The group members further stated that they will determine the location and timing of the battle with Hezbollah in Lebanon, and appealed to the public to stay away from places associated with Iran and Hezbollah in order to stay safe from future attacks.

Thursday's blast comes six weeks after a car bomb attack in the same area wounded more than 50 people.

Another little-known Syrian rebel group, the Special Forces 313 Brigade, claimed that attack and said it was in revenge for Hezbollah fighting alongside the Assad regime.

The mainstream rebel Free Syrian Army condemned the attack, according to AFP.

Lebanese president Michel Sleiman was quick to blame Israel for Thursday’s attack, saying, “This is a criminal act that bears the fingerprints of terrorism and Israel and is aimed to destabilize Lebanon and deal a blow to the resilience of the Lebanese.”

Lebanese Parliament Speaker Nabih Berri also blamed Israel and urged the Lebanese to unite in the face of dangers. “This crime only serves the Israeli enemy that is working on dealing a blow to the components of national unity in Lebanon,” Berri said.