It was a rare show of unity for this conservative kingdom, where Shiites are a minority seen as heretics by some clerics of the conservative Sunni sect of Wahabism that dominates the country.
"This heinous crime, and all other violent attacks that preceded it ... aim to create sedition among Muslims and divide them, and consolidate the pretexts for the presence of occupation forces in Iraq," said the statement signed by Sunni reformists and Shiite public figures.
The statement, a copy of which was received by The Associated Press, expressed condolences to Iraqis and called for a unified stance against the "challenges and dangers facing the Muslim nation and unity ... to face extremist ideas."
The attacks by suicide bombers and pre-set explosives struck on Ashoura, the holiest day of the Shiite calendar, when tens of thousands of people were gathered in Karbala and at Baghdad's Kazimiya shrine to mark the 7th century martyrdom of Imam Hussein, the prophet Muhammad's grandson.
Jafar Shayeb, a Shiite businessman and activist who signed the statement, said the attacks were part of a trend that wants to use developments in Iraq to divide Muslims across the Arab world.
"Everyone feels that there are parties that will benefit from causing division among Muslim society, and this will reflect here," he said.
Shiites, who represent about 10 percent of the kingdom's 20 million people, have recently been outspoken about discrimination against them in both official Saudi Arabia, and among conservative clerics, who shun not only other religions but also other Muslim sects.
Wahabi clerics have often spoken out against Shiite rituals, the most prominent of which is Ashoura.