The senior Shiite cleric in Bahrain Sheikh Isa Qassim has criticized the Gulf kingdom's Sunni rulers for practicing what he says is "fake democracy" ahead of parliament elections.

Bahrain stages by-elections Saturday boycotted by the main Shiite opposition bloc, with pro-democracy protesters vowing to escalate their actions six months after an uprising in the kingdom was crushed.

The elections are for 18 seats left vacant in the 40-member parliament after MPs from Al-Wefaq, the Gulf state's largest opposition group, quit in February in protest over a crackdown by security forces on peaceful demonstrators.

Bahraini authorities later allowed protesters, mostly Shiites, to camp out at Manama's central Pearl Square until security forces, boosted by a Saudi-led Gulf regiment, drove them out in a deadly crackdown in mid-March.

As tension soared in Bahrain, home to the US Fifth Fleet, US President Barack Obama's pick for ambassador urged the kingdom Wednesday to avoid "repression."

"Political reform and respect for human rights are vital to Bahrain's stability and to the protection of US interests in the region," Thomas Krajeski told a Senate Foreign Relations Committee confirmation hearing.

"Bahrain's long-term stability depends on addressing domestic grievances not through repression, but through genuine reform and reconciliation."