The Pentagon last week notified Congress of the proposed sale of armored vehicles and wire-guided missiles to Bahrain, the first since the Sunni-led kingdom was rapped for its response to a Shiite uprising early this year.
Maria McFarland, deputy Washington director at Human Rights Watch, said the proposed sale makes it hard for the international community to take the United States seriously when it speaks of democratic reform in the region.
"This is exactly the wrong move after Bahrain brutally suppressed protests and is carrying out a relentless campaign of retribution against its critics," she said in a statement.
Washington was criticized for taking a soft stance on the kingdom's crackdown on the Shiite opposition movement. Bahrain hosts the U.S. Navy's 5th Fleet.
The Human Rights Watch complaint comes amid reports that security forces fired tear gas and rubber bullets at protesters calling for a boycott of weekend parliamentary elections.
"The protesters have tried to take to the streets in a number of villages around the country and they have been immediately met with brutal police repression," a source in Bahrain told al-Jazeera.
Bahrain has touted its reforms since the uprising early this year. The weekend elections are to fill seats left empty when Shiite opposition groups quit the government in protest.