The lawmakers told Kerry they are "deeply alarmed" by the government of Bahrain's suppression of free speech and political dissent.
The senators want Kerry to tell them what specific actions the Obama administration is taking to press the government of Bahrain "to return to a path of reform and reconciliation."
The tiny island kingdom of Bahrain hosts the Navy's 5th Fleet. In the last few weeks, the senators wrote , Bahrain's Sunni monarchy has "taken a series of troubling steps targeting the country's peaceful opposition, as well as nonviolent human rights defenders and members of civil society."
In one example, the senators cited a Bahraini court's decision to more than double a prison term for the secretary-general of the country's largest Shiite opposition group, Al-Wefaq.
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Bahrain also detained Nabeel Rajab, a prominent activist and the president of the Bahrain Center for Human Rights, on a charge of spreading "false news."
Bahrain's government crushed the Arab Spring protests in early 2011 with the help of troops from Saudi Arabia and the United Arab Emirates.
A top general in Shiite-majority Iran has threatened the "destruction of the bloodthirsty regime" in Manama, Bahrain's capital and largest city.
The senators said there is risk of the country spiraling into violence and "further exploitation" by Tehran unless Bahrain's government changes course.