BEIRUT, Lebanon — The bomb that tore through downtown Beirut on Friday killed a former Lebanese finance minister who was a prominent critic of the Syrian government — an attack that unleashed a storm of political recriminations that threaten the fragile entente keeping the Syrian war from spilling outright into Lebanon.

The former minister, Mohamad B. Chatah, was one of the closest advisers to Saad Hariri, son of former Prime Minister Rafik Hariri, another opponent of the Syrian leadership whose assassination in a 2005 bombing touched off the March 14 protest movement that helped end Syria’s 29-year military presence in Lebanon.

On Friday, Saad Hariri, himself a former prime minister, and his March 14 political allies quickly issued statements implying that the Syrian government or its ally Hezbollah was responsible for the bombing, which killed at least six people and wounded dozens, and drew parallels to the killing of Rafik Hariri, for which the international Special Tribunal for Lebanon has indicted four Hezbollah operatives.

The allegations were electric in a country that is deeply divided over Syria, with Mr. Hariri’s Future bloc, the main Sunni party, backing the opponents of President Bashar al-Assad, and with Hezbollah, the Shiite militia that is also Lebanon’s most powerful political party, supporting him.