BAGHDAD – Bombs pounded six Iraqi cities and towns Tuesday, killing at least 40 people and raising suspicion that security forces might be assisting terrorists in launching attacks on Shiite Muslims.

The onslaught came just ahead of a religious pilgrimage that could attract even more violence.

A senior Iraqi intelligence official said checkpoint guards may have been bribed to help al-Qaida-linked Sunni insurgents plant bombs at Shiite marketplaces. The attacks injected new fear into Iraqis, resigned to worsening violence six months after the last American troops left the country.