By Kevin Anderson and Nick Childs
BBC correspondents in Washington
European families of the detainees held at the US military base at Guantanamo Bay Cuba came to Washington to denounce the treatment of their relatives and to urge President George W Bush to respect their legal rights.
Azmat Begg came to Washington to ask for justice for his son
In front of the US Supreme Court, they called on the US to respect its own ideals of "equal justice under law".
They joined US religious groups in saying that their relatives had been banished to a legal limbo, a Kafka-esque travesty of justice where they were not told the charges against them.
The Pentagon continued to defend its policy, saying that the detainees are being held just as prisoners in previous conflicts were.
'No law zone'
"We are here because the principle of due process under the law is also being held prisoner on Guantanamo," said Robert Edgar, general secretary of the National Council of Churches USA.
Between 640 and 660 Taleban and al-Qaeda suspects are being held at Guantanamo Bay, and he called for the detainees either to be charged and tried or to be released for lack of evidence.
"No place in the world should be set up as a 'no-law' zone," he said.
Among the family members of the detainees who travelled to Washington was Azmat Begg, father of British detainee Moazzam Begg.
He read a letter he hoped to deliver to President Bush.
"Mr President, I do not plead for mercy. My son has not been charged with any crime," he said, adding, "I do not ask for mercy. I ask for justice. Before mercy comes justice, and my son has been denied justice."
Mr Begg also asked that his son be afforded basic human rights. "He wrote that he is being kept like an animal in a cell," Mr Begg told the small crowd.
Moazzam was not included in five Britons set for release, and Mr Begg asked President Bush to tell him what obstacles remained to his son's release.
The relatives were joined by former hostage Terry Waite and actors Corin and Vanessa Redgrave.
Mr Redgrave said that the Americans have afforded Saddam Hussein prisoner of war status but have not offered it to a single one of the Guantanamo detainees.
"That seems to be a glaring example of inequality under international humanitarian law," he said.
Mr Waite said the detentions was "doing fundamental harm to the image of America overseas, and in fact, in my opinion... is likely to increase terrorism by sending more people to the extreme edges."
The families had hoped to meet with President Bush, but instead had to settle for a march to the White House where the religious leaders prayed and made brief statements in an icy rain.
Robert McIlvaine, who lost his son in the attacks of 11 September, joined the march.
"I'm speaking up as a citizen to say that what we are doing is wrong," he said, adding, "It's breaking every international law that exists. Everybody has a right to justice."
The debate continues
The Pentagon continues to defend the detentions, saying critics misunderstand the situation.
Pentagon officials say that the detainees are not at Guantanamo Bay for criminal punishment, but as enemy combatants in an ongoing war.
Separately, the Pentagon says, some may face war crimes trials under a new military tribunals system.
The detainees have been held for two years without trial
Critics contend that the administration has been picking and choosing what rules do and don't apply to the detainees, and even friendly governments have been unhappy with the process.
There have been tensions within the Bush administration, too, not least between the Pentagon and the state department, including over how long it has taken to establish the new tribunals.
Others complain that the Pentagon's position means that detainees who it considers a threat could be held indefinitely, as there's not even any clear idea of how this so-called war on terrorism might be brought to an end.
That, the critics argue, is another distinction between this and other conflicts which makes the official US position untenable.
The controversy within the United States may be more muted than it is outside - many Americans sympathise with the evident frustration of the Bush administration that the detainees are widely portrayed as innocents rather than potential security threats.
Again, the critics say the administration has provided no evidence, just assertions. The controversy is unlikely to die down, but the debate is likely to move on as the first tribunals finally get under way, probably in the next few months.