A simmering political crisis in Bahrain could spiral into violence, encourage meddling by Iran and weaken a key U.S. ally in the Persian Gulf, a bipartisan group of senators warned Thursday in a letter to Secretary of State John Kerry.

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." Unless those actions are reversed, they told Kerry, "we fear that tensions in Bahrain could quickly intensify and destabilize an important United States ally."

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. 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. Since then, the island has seen low-level unrest, protests and attacks on police.

But while the protests five years ago saw the island's Shiite majority and others rise up to demand more political freedom, the current crackdown has seen a growing level of sectarianism. 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.

"Bahrain's failure to address the legitimate grievances of its citizens has strained the country's social fabric and invited outside actors to take advantage of the deteriorating situation," they wrote.

A State Department report sent to Congress last week said Bahrain has fallen short in implementing a series of political and human rights reforms recommended by an independent commission after the 2011 uprisings.

The report cited progress in several areas but said failures in others diminishes the improvements and minimizes "popular acceptance of newly established government institutions."

Sen. Ron Wyden, D-Ore., and Rep. James McGovern, D-Mass., introduced legislation last year to prohibit the United States from selling Bahrain weapons and crowd control equipment until the State Department certifies that all of the commission's recommendations have been put into action.

Sen. Chris Murphy, D-Conn., led the letter, which also is signed by Wyden, Marco Rubio, R-Fla., Patrick Leahy, D-Vt., Robert Casey, D-Pa., Chris Coons, D-Del., and Tim Kaine, D-Va.

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