American Sikhs and their supporters in Congress on Thursday praised the military for easing a ban on beards but called for an outright decision to allow their articles of faith.

The Pentagon on Wednesday loosened its requirement for soldiers to be "clean-cut," which ruled out most service by devout Sikhs whose religion requires men to don turbans and beards.

The new policy calls on all US military departments to "accommodate religious requests of service members unless they have an adverse effect on military readiness, mission accomplishment, unit cohesion, and good order and discipline."

The Sikh Coalition said it was "deeply appreciative" for the Pentagon's work. "We are disappointed, however, that the presumptive ban on Sikh articles of faith remains intact," the advocacy group said in a statement.

Representative Joe Crowley, a leading advocate for the community, said the changes "may be a step in the right direction" but said that inclusion of Sikhs should not be a case-by-case matter.

"Sikh Americans love this country and want a fair chance to serve in our nation's military," said Crowley, a Democrat from New York City.

Crowley and fellow members of Congress, including members of the rival Republican Party, wrote a letter to Defense Secretary Chuck Hagel to urge further action.

They pointed to three Sikh soldiers who served with distinction in the US military in recent years after receiving permission to maintain their articles of faith.

"Given the achievements of these soldiers and their demonstrated ability to comply with operational requirements while practicing their faith, we believe it is time for our military to make inclusion of practicing Sikh Americans the rule, not the exception," the letter said.

Several countries including Britain, Canada and India allow Sikhs to serve in uniform.

Sikhs, whose religion was founded five centuries ago in South Asia, have faced frequent attacks in the United States due to their appearance. In August 2012, a white supremacist shot dead six Sikhs after barging into their temple in Wisconsin.