A Muslim civil rights group on Friday accused the US government of forcing an American citizen into "exile" because he was an Islamic convert.

The Washington-based Council on American-Islamic Relations (CAIR) said Raymond Earl Knaeble IV, 29, had been placed on a no-fly list and had been unable to return home from Colombia since March.

The group's claim could not be independently confirmed and the Department of Justice did not immediately respond to a request for comment.

According to CAIR, Knaeble this week flew to Mexico in hope of travelling to the Mexican-US border, but he instead faced lengthy interrogation by Mexican officials before being sent back to Colombia.

"He was stopped by Mexican authorities as he got off the plane and asked, 'Are you Muslim?' He was then detained for 15 hours and asked many questions relating to his faith," according to CAIR.

"It is un-American and illegal for a citizen who has not been accused of, let alone charged with, any crime to be denied entry to his own country without adequate explanation," said CAIR lawyer Nadhira Al-Khalili, who is representing Knaeble.

"We call on the Department of Justice to end Mr Knaeble's forced exile and to address the disturbing issue of the other Americans who are similarly being denied re-entry to their own country," she said.

The controversy over Knaeble comes as political pressure grows in Washington for US citizens to be stripped of many rights if they are believed or found to be involved with Islamist militants.

The calls come in response to fears that underground militant groups are recruiting US citizen Muslims to strike at US targets without having previously attracted attention.

However, human rights campaigners say these proposals undermine the US Constitution.

Last week, a group of US lawmakers unveiled legislation seeking to remove citizenship from Americans thought to have joined hardline groups like Al-Qaeda, arguing that this would then allow US forces to assassinate them freely.