Bahrain Mirror- AFP: The United States on Wednesday voiced concern over ally Bahrain's sentencing of the head of the country's Shiite opposition movement, although it stopped short of threatening countermeasures.

"The United States is concerned by the verdict sentencing Ali Salman to life in prison in Bahrain," State Department spokesman Robert Palladino told reporters.

"The United States will continue to engage regularly with the government of Bahrain on a range of shared interests, including the importance of safeguarding fundamental freedoms and human rights," he said.

Bahrain on Sunday sentenced Salman, who headed the now-banned Al-Wefaq movement, to life in prison for allegedly spying on behalf of rival Gulf state Qatar.

Ruled for more than two centuries by the Sunni Al-Khalifa dynasty, Bahrain has been hit by waves of unrest since 2011, when security forces crushed protests from the Shiite majority demanding a constitutional monarchy and an elected prime minister.

The Gulf island-state is a vital link for Western militaries. It is the home of the US Navy's Fifth Fleet, which patrols the oil-rich region, as well as a permanent British base.

President Donald Trump has made clear that he will not restrict arms sales to allies, pointing to the job and security benefits.

The Trump administration lifted restrictions on arms sales to Bahrain that former president Barack Obama imposed on human rights grounds.

US rival Iran, ruled by Shiite clerics, also condemned the sentence of Salman which it said showed Bahrain's plans to "intensify its suppression."