MANAMA, Bahrain (AP) :Bahrain's top Shiite cleric on Friday sharply criticized the life sentences given to eight opposition leaders by a special security court for their role in anti-government protests. Sheik Isa Qassim's sermon is the latest signal that Shiite leaders could snub appeals by Bahrain's Sunni rulers for dialogue next month amid the crackdown on opposition supporters in the Gulf kingdom, which is home to the U.S. Navy's 5th Fleet. The cleric called the mass trials of Shiite opposition figures unfair and appealed to the nation's Sunni rulers to overturn the sentences if they want dialogue. Bahrain on Wednesday convicted 21 opposition figures of plotting to overthrow the royal family. Eight leaders received life sentences and 13 others got long prison terms. "This is not an environment for a political solution, when people are suffering," the cleric said during the Friday sermon in Diraz, an opposition stronghold northwest of the capital, Manama. "These sentences and abuses are like a dam preventing people from participating in dialogue." Bahrain's ruling dynasty has proposed opening talks with opposition delegates July 1, but the outreach has met a cool reception from Shiite leaders demanding that authorities roll back security measures and halt trials against activists and others on anti-state charges. At least 31 people have died in the unrest and hundreds have been detained since February when Bahrain's Shiite-led campaign for greater freedoms and more rights began. The security court that was set up under martial law, imposed in March to quell protests, has promoted criticism from Bahrain's Western allies. The U.S. expressed concern about the severity of the sentences and the use of the military-linked security courts. U.N. Secretary-General Ban Ki-moon urged Bahrain's government to allow political activists involved in the Arab Spring opposition movement to appeal their harsh sentences.