BAGHDAD, Iraq — A suicide car bomber turned a venerable book market into a deadly inferno and gunmen targeted Shiite pilgrims Monday as suspected Sunni insurgents brought major bloodshed back into the lap of their main Shiite rivals. At least 38 people died in the blast and seven pilgrims were killed.

The violence — after a relative three-day lull in Baghdad — was seen as another salvo in the Sunni extremist campaign to provoke a sectarian civil war that could tear apart the Shiite-led government and erase Washington’s plans for Iraq.

The Shiite Mahdi Army militia has so far resisted full-scale retaliation through a combination of self-interest and intense government pressure. But the militia’s leader, the radical cleric Muqtada al-Sadr, is now being cornered in new ways that have put him on the defensive.

An expected Cabinet reshuffle could take a serious bite out of al-Sadr’s voice in government — a move strongly encouraged by Washington.

Al-Sadr also opened the door for U.S. and Iraqi troops to enter the Mahdi stronghold of Sadr City in Baghdad — under a painstaking deal with authorities — but his loyalists are still being hunted outside the capital.

“Al-Sadr and his forces could be feeling under siege,” said Alireza Nourizadeh, chief researcher at the London-based Center for Arab-Iranian Studies. “That makes them less predictable. That means they are more dangerous.”

One possible sign of brewing troubles was 30 bullet-ridden bodies found across Baghdad. Many of those killings are blamed on Shiite death squads, and Monday’s figure was the highest in weeks.

And the Sunni extremists keep pressing.

The suicide mission tore through booksellers and other stores on narrow Mutanabi Street, a mostly Shiite-run commercial area in Baghdad’s historical heart along the Tigris River.