The visit comes less than a week after Bahrain's crown prince called for new efforts for talks between the Sunni leadership and the kingdom's majority Shiites, who seek a greater political voice.
Inese Vaidere of Latvia told reporters Thursday that authorities should free all "prisoners of conscience" as a crucial step toward negotiations in the 22-month uprising.
Vaidere said the European team met with jailed opposition leaders including Abdulhadi al-Khawaja, who has been sentenced to life in prison.
More than 55 people have died in Bahrain's near nonstop unrest since February 2011. Bahrain is home to the U.S. Navy's 5th Fleet.