A Muslim prisoner has been granted the right to grow a beard after a court ruled that his religious rights trumped security concerns.

The Arkansas Department of Correction had previously banned prisoners from growing beards, citing fears that weapons or contraband could be hidden within them. The state had also suggested that escaped prisoners could easily change their appearance by shaving.

However, in a unanimous vote yesterday, nine Justices dismissed this argument. "Hair on the head is a more plausible place to hide contraband than a half-inch beard, and the same is true of an inmate's clothing and shoes," Justice Samuel Alito said.

"Nevertheless, the department does not require inmates to go about bald, barefoot or naked."

Alito added: "We readily agree that [the state] has a compelling interest in staunching the flow of contraband into and within its facilities. But the argument that this interest would be seriously compromised by allowing an inmate to grow a half-inch beard is hard to take seriously."

Alito also said the state already searches clothing and hair and had not given a valid reason why it could not also search beards.

The prisoner in question, Gregory Holt – otherwise known as Abdul Maalik Muhammad – said his case was "a matter of grave importance, pitting the rights of Muslim inmates against a system that is hostile to these views".

He argued that the state's prison grooming policy prohibiting inmates from having facial hair other than a "neatly trimmed mustache" violated his religious rights under a 2000 federal law called the Religious Land Use and Institutionalized Persons Act.

His lawyers noted that more than 40 states and the federal government allow prison inmates to have similar beards.

Eric Rassbach, Deputy General Counsel for the Becket Fund for Religious Freedom labelled the ruling "a huge win for religious freedom and for all Americans".

"What the Supreme Court said today was that government officials cannot impose arbitrary restrictions on religious liberty just because they think government knows best," he said.

The court's decision has been compared to last year's judgement on the Hobby Lobby case, where it was made legal for closely-held businesses to uphold religious objections which allow them to opt out of contraceptive health law requirements.

Justice Ruth Balder Ginsburg yesterday distinguished between the two cases, however. "Unlike the exemption this court approved (in Hobby Lobby), accommodating petitioner's religious belief in this case would not detrimentally affect others who do not share petitioner's belief," she said in a concurrence.

Holt, who wanted to grow a half-inch beard, is serving a life sentence for burglary and domestic battery at the Varner Supermax prison. In 2005, he pleaded guilty to separate charges of threatening the daughters of then-President George W Bush.

(Additional reporting by Reuters)