The death toll from a car bomb which ripped through the southern Beirut stronghold of Lebanon's militant group Hezbollah rose on Friday to 24, and the government said it was investigating whether the blast was a suicide attack.Interior Minister Marwan Charbel said investigators were checking CCTV footage in the moments before the explosion to see whether the van which was believed to be carrying the bomb had been driven by a suicide bomber or detonated remotely."The first hypothesis is that the driver blew himself up, while the second hypothesis says that the car may have been blown up from a distance," Lebanon's National News Agency quoted Charbel as saying. Reporters who arrived at the scene minutes after the explosion saw a burnt-out car near the center of the road, suggesting it was being driven when it blew up.While a Sunni Islamist group claimed responsibility for the bombing, Hezbollah and Lebanese officials said it bore the markings of a Zionist attack and served the interests of Israel.A Sunni Islamist group calling itself the Brigades of Aisha claimed responsibility for the explosion, saying it targeted Hezbollah and promising more attacks.Lebanese Interior Minister Marwan Charbel suggested that the attack may have been Israeli retaliation for explosions that wounded four Israeli soldiers who allegedly infiltrated southern Lebanon last week.Senior Hezbollah figures said that the blast "has Zionist fingerprints all over it." On Friday, however, Hezbollah leader Hassan Nasrallah said that radical Sunni Islamists were likely to have been responsible for the bomb.Nasrallah said earlier attacks against the Iranian-backed Shi'ite Muslim group's Beirut base and other Shi'ite areas in Lebanon were the work of "takfiri" factions, in reference to Sunni radical groups linked to al-Qaida.Israel denies involvement in attackMeanwhile, Israeli leaders on Friday vehemently denied a claim by Lebanese President Michel Suleiman that Israel was behind the attack. "Israel has no ties to the situation in Lebanon, we want to see a stable and united Lebanon," President Shimon Peres said during a meeting with UN Secretary-General Ban Ki-moon. "I was surprised that Lebanon's president again accused Israel as responsible for a terrorist attack. I ask why he looks in Israel's direction when in his territory Hezbollah is accumulating bombs and missiles," he said. Former Mossad chief Danny Yatom also discounted Suleiman's claim. “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 media quoted Suleiman as saying on Thursday.Yatom stated that the bombing, in which 20 people were killed and more than 212 were injured, was an internal Lebanese matter of state and denied Israel's involvement as it has "enough problems of [its] own"."We have become accustomed to this kind of accusations, they need to be ignored," Yatom told Army Radio on Friday. "There is almost no situation in the Middle East that Israel's opponents do not attribute to Israel, and this is also true in this case," he said.Sectarian tensions have been high in Lebanon following the intervention of Shi'ite Muslim Hezbollah in support of Syrian President Bashar Assad against a two-year revolt led by Syria's Sunni Muslim majority. Hezbollah also fought a month-long war with Israel in 2006.