LONDON (Reuters) - Britain has “some concerns” about whether the trial of the alleged mastermind of the September 11 attacks will respect his legal rights, Foreign Secretary David Miliband said on Tuesday.

The Pentagon on Monday announced charges against Khalid Sheikh Mohammed and five other detainees imprisoned at the U.S. detention centre at Guantanamo Bay, Cuba.

The charges include conspiring with al Qaeda to attack and murder civilians and 2,973 counts of murder for those killed. The Pentagon is seeking the death penalty.

Asked on a BBC Radio phone-in show if he believed the trial of Mohammed, a Pakistani national, would respect his legal rights, Miliband said: “We have some concerns about that.”

“There are still some cases in front of the American Supreme Court, because, of course, the great thing about America ... is that the independent legal system provides a check and a balance on the operation of the legal system itself,” he said.

Miliband said the Supreme Court had already ruled against some of the tribunals that have been set up to try Guantanamo detainees.

“There are some cases in respect of what’s called the Military Commissions Act, which is the basis on which he’d be tried, that are being discussed in front of the Supreme Court at the moment,” he said on BBC2’s Jeremy Vine show.

Mohammed is reported to have admitted planning every aspect of the September 11 attacks, but there could be a problem if such a confession were used as evidence because the CIA has admitted it subjected him to “waterboarding” -- an interrogation technique simulating drowning that has been widely criticized as torture.

The rules of the court on the U.S. naval base at Guantanamo Bay, Cuba, prohibit the use of evidence gained through torture, as does an international treaty the United States has signed.

Miliband said there was “absolutely no question” torture was illegal. Britain defines water-boarding as torture, he added. “We don’t ... we would never use water-boarding”.

“There’s absolutely no question about the UK government’s commitments in respect of torture, which is illegal, and our definition of what torture is,” he added.

“And I think it’s very, very important that we always assert that our system of values is different from those who attacked the U.S. and killed British citizens on 11 September, and that’s something we’d always want to stand up for.”

Former prime minister Tony Blair came under fire from members of his own Labour Party for not being critical enough of U.S. President George W. Bush over the Guantanamo Bay detention centre.