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.

“We want to live a normal life, but with the current spike in violence and victims, I am personally thinking of moving,” said Hassan al-Saadi, 40, a Shiite store owner in Baghdad who is considering pulling his four children from school for their safety.

A spike in violence over the last month is blamed partially on Iraq’s paralyzing political crisis, which pits Prime Minister Nouri al-Maliki’s Shiite-led government against rival Shiite politicians, Sunni Muslims and ethic Kurds who complain that they have been sidelined.

Tuesday’s deadliest attacks hit the Shiite cities of Karbala and Diwaniyah. Despite the risk, hundreds of thousands of Shiite pilgrims are expected to gather Friday in Karbala for an annual religious observance.