Iraqi authorities say 50 suspected insurgents have been detained in connection with Sunday's suicide car bombings in the nation's two holiest Shi'ite cities, Najaf and Karbala.

Hospital officials say the death toll from the carnage has risen to 66 - at least 52 lives lost in Najaf and 14 in Karbala. More than 140 people were wounded by the explosions.

Shi'ite Muslim leaders have appealed for calm, saying such attacks are clearly attempts to ignite sectarian violence and prevent Iraq's first post-Saddam elections, scheduled to take place in six weeks, on January 30.

Shi'ite leaders are urging their followers not to resort to revenge attacks, but to focus on the upcoming national elections.

Some information for this report provided by AP and Reuters.