Human rights groups are fighting a proposed American sale of $53 million worth of weapons to the tiny Arab nation of Bahrain, whose monarchy has cracked down forcefully on a protest movement that saw thousands take to the streets earlier this year.

The Defense Department notified Congress on September 14 of a plan to sell equipment including 44 Humvees, more than 50 bunker-buster missiles and night-vision technology for the army of the island nation.

Pentagon officials noted in an accompanying document that the weapons would improve the security of a major ally, “that has been, and continues to be, an important force for political stability and economic progress in the Middle East.” The navy’s Fifth Fleet, whose area of operations covers such strategic areas as the Arabian Gulf and the seas around Yemen, is based in Bahrain, where there has been an American naval presence since 1971.

After thousands of demonstrators occupied Pearl Roundabout in the capital Manama in February, security forces killed 20 people and arrested thousands more, according to Human Rights Watch.

The monarchy has said that they have been “seeking to fairly balance out the need to maintain law and order with the desire for freedoms,” while also conducting dialogue with some of the protest groups. But criticism of its actions has been widespread.

In May, President Obama said that the authorities had used, “mass arrests and brute force.” The State Department expressed, “deep concern about the detention of civil society leaders and opposition politicians, as well as Bahraini moves to clamp down on opposition political activities and independent media.”

“We are very surprised that the U.S. would decide that now is a good time to reward the Bahraini dictatorship with weapons,” said Brian Dooley, a director at the Washington-based Human Rights First.

“This is a brutal crackdown by any standards,” added Dooley, who has traveled to Bahrain twice this year. “It’s the riot police who have been most visible on the streets shooting peaceful protestors, but the army have committed plenty of human rights abuses themselves.” Dooley said that the army had been responsible for torture of detainees being interrogated.

Human Rights First is one of 13 organizations to submit a letter to Congress requesting that they block the deal, citing human rights issues and concerns that the sale would affect public sentiment toward the U.S. and its presence in Bahrain.

A State Department official said that the U.S. government weighs the economic, national security, foreign policy and human rights implications of any proposed transfer of arms very carefully.

Speaking on the condition of anonymity to discuss sensitive policy matters, the official added, “We view the proposed sale as one that would help Bahrain’s defense force develop its capabilities against external threats and would ensure interoperability with our forces.” The official also said that the government continues to engage with Bahraini authorities to promote reconciliation and respect for human rights.