“For the first time, we feel that it is the regular Lebanese citizen who is being targeted in this explosion and, maybe, this is the beginning of what Syrian authorities have promised us in the past,” said Nadim Gemayel, a member of Parliament from the Christian Phalange movement that is part of Lebanon’s opposition March 14 bloc. “The Syrian regime had talked about burning everything in their path.”

As news spread of the bombing, the streets of Beirut’s largely Christian Ashrafiyeh district were initially calm. People walked dogs and escorted children home from school. But they also gathered in small groups warily discussing the bombing and clutched cellphones to share news. Outside a damaged grocery stood Sandra Abrass, a filmmaker and former Red Cross worker, frustrated that she was not allowed to help on the scene because her skimpy yellow flats were no protection against broken glass, and said she was in pain first for the wounded and then for Lebanon.

“You don’t feel safe any more,” she said. After growing up during the 1975-1991 civil war, she said, she was no longer used to the idea that bombs could go off at any moment, and feared that there would be more bombings and reprisals.

“They cannot let us live happily,” she said.

General Hassan came to prominence as a security chief for the assassinated former prime minister, Mr. Hariri. Early on, he was a suspect in that killing, but later helped build a circumstantial case, based on phone records, that a team from Hezbollah, the militant Lebanese Shiite organization aligned with Syria, had coordinated the Hariri attack and was at the scene of the murder. Hezbollah, which has since become an important member of Lebanon’s government, claims the records were fabricated.

Another security official, Wissam al-Eid, who helped compile the phone records, was killed in a car bombing in 2008, part of a series of assassinations of political figures, journalists and investigators.

More recently, in August, General Hassan shocked Lebanon by arresting a prominent pro-Syrian politician, Michel Samaha, on charges of importing explosives in a bid to set off bombs and wreak sectarian havoc as part of a Syrian-led plot. It was a surprising move in a country where state institutions have rarely had the power to take on political figures, especially those backed by foreign powers or Lebanese militias.