The main Shiite opposition bloc in Bahrain says its head has been arrested in a move that could inflame tensions in the tiny Western-allied Gulf kingdom.

Al Wefaq says it considers its leader, Ali Salman, to be under arrest hours after he was called in for questioning in what it alleged was a "series of illegal measures" by authorities.

Bahraini officials did not issue any comment on Salman or immediately respond to questions.

Al Wefaq has been a major driver in Arab Spring-inspired protests that began in February 2011 in the strategic island nation, which is home to the U.S. Navy's 5th Fleet. More than 65 people have been killed since the unrest began against the Sunni-led monarchy. Some rights groups place the overall death toll higher.