BAGHDAD, April 12 — A suicide bomber wearing an explosive vest struck deep inside the heavily fortified International Zone on Thursday, killing eight people when he detonated inside the Parliament building just a few feet from the main chamber.

In a separate and in some ways equally traumatic attack early in the day, a truck bomb destroyed the beloved, 60-year-old Sarafiya bridge across the Tigris and killed six people. The heavily traveled bridge has long been a symbol of Baghdad, illustrated on old postcards and drawings of the city from a more peaceful time.

The attack on the Parliament was the worst bombing to take place in the International Zone since the protected area was established four years ago, when it was known as the Green Zone. At a time when Iraqis are increasingly questioning the government’s ability to protect them, the bombing raised the troubling possibility that it cannot even fully protect itself, although it is at the wellspring of American and Iraqi military power in the city.

The bomber struck a half hour after the day’s session had closed, in a cafe area where lawmakers were lingering across from the main chamber. Among the dead were at least two lawmakers, both from Sunni Arab parties. Of the 23 people wounded, 11 were parliamentarians, the United States military reported.