BEIRUT, Lebanon — A bomb tore through a crowded neighborhood in Damascus on Friday, killing 26 people and wounding dozens more, unleashing scenes of chaos and underlining the growing confusion and complexity of the Syrian uprising, officials and residents said.

The bombing was the second in two weeks in the fortified capital, though no one has claimed responsibility for either. An uprising that began relatively peacefully in March has grown markedly more violent, with Friday’s bloody episode and bolder insurgent attacks punctuating a landscape roiled by antigovernment protests that again showed new momentum.

In style at least, the bombings themselves recalled a revolt in the late 1970s and early 1980s, when an Islamist insurgency marked by bombings and large-scale killings posed a sweeping challenge to the rule of Hafez al-Assad, the father of Syria’s current president, Bashar al-Assad.

“A known political party was behind the attacks in those years,” said Louay Hussein, a prominent opposition figure in Syria, who was reached by telephone. “Today, we don’t know who is behind these attacks, and this represents a great danger.”