Iraqi Col. Ali Jraiwi said the captured insurgents told Najaf police they are members of a group called "Soldiers of Heaven" and are a mix of Sunni and Shiite Muslims that believe eliminating the clerics would bring about a new Muslim messiah, CNN reported.
Officials said the insurgents planned to seize control of Najaf and the surrounding province.
Among their targets was Grand Ayatollah Ali al-Sistani, whose death "would really plunge Iraq and the possibly the rest of the region into a bloodbath," said Vali Nasr, who studies Shiite influence in the Middle East.
The military push against them peaked on Sunday, when at least 200 fighters were killed, 120 were captured and 60 others wounded, Iraqi Defense Ministry spokesman Mohammed al-Askari said. He said six Iraqi soldiers were killed and another 30 wounded in Sunday's fighting.