- Hezbollah leader Hassan Nasrallah is scheduled to address a large rally
- The Lebanese army says a car bomb caused the blast
- An unknown group claims responsibility in a YouTube video
- The area is a Hezbollah stronghold
Lebanese authorities Friday raised the death toll from a car bombing the day earlier, saying at least 22 people were killed and hundreds injured in a southern suburb of Beirut.
Thursday's bomb rocked an area known as a stronghold of the Lebanese Shiite militant group Hezbollah, the Lebanese army said.
At least 228 others were injured in the terrorist attack, the Lebanese Internal Security Forces said.
There was a heightened security presence Friday in Beirut and other areas of Lebanon, but tensions appeared lower than on Thursday evening.
Hezbollah leader Hassan Nasrallah is due to address a large rally Friday in the southern Lebanon town of Aita al Shaab, close to the border with Israel.
It's unclear if Nasrallah will respond to the bombing, which appeared to target Hezbollah, and whether, if so, his words will provoke more anger against the movement and its involvement in Syria's civil war.
The previously planned rally is being held to mark the seventh anniversary of Hezbollah's July 2006 war with Israel.
Along with Shiite-dominated Iran, Hezbollah is helping Syria's government fight rebels, whose ranks are dominated by Sunnis.
After Thursday's blast, a YouTube video surfaced in which three masked men holding weapons claimed they are part of a group responsible for the attack. They stood before a large Arabic sign containing the Islamic creed, "There is no God but Allah, and Mohammed is the messenger of Allah."
The group, which calls itself the Brigade of Aisha, Mother of Believers, accused Hezbollah of being aggressors. Aisha, the last wife of the Prophet Mohammed, is especially revered by Sunni Muslims.
In its YouTube post, the group called Nasrallah a "pig" and said he works on behalf of Iran and Israel.
"A message: To our brothers and sisters in Lebanon: Stay away from anything to do with Iran -- whether in Beirut or outside Beirut," it said.
CNN could not confirm the authenticity of the video or the men's claims. The U.S. Embassy in Beirut tweeted condemnations of the attack.
Hezbollah's involvement in the Syrian conflict has angered some in Lebanon, and many Lebanese fear that the group could be the target of more attacks in future.
People living near the scene of Thursday's blast told CNN they worried that if a car bomb could be brought into this neighborhood, which Hezbollah tightly controls, then others might follow.
Many Lebanese see the attack as another indication that Syria's civil war is spilling over its borders. Lebanon is divided along the same sectarian lines as its neighbor.
Lebanon's army said its units responded immediately to the bombing Thursday evening, setting up a security zone and beginning investigations.
Civil defense units were trying to rescue some citizens stuck inside their homes due to the fire resulting from the blast, Lebanon's National News Agency reported.
The explosion came about a month after a car bomb injured dozens of people in the pro-Hezbollah neighborhood of Bir El Abed in a southern Beirut suburb.