Nichols could still face a state trial

Nichols is currently serving a life sentence for conspiracy and involuntary manslaughter. He helped to plan the 1995 bombing in which 168 people were killed.

McVeigh was convicted as the one who masterminded the attack, and was executed in June after dropping an appeal also based on the FBI documents.

Lawyers for Nichols had been trying to get him a new trial after the FBI revealed that it had withheld thousands of pages of evidence from the original trial.

They said the new documents strengthened their argument that prosecutors mishandled information that could have helped their client before the trial.

McVeigh was executed for his part in the bombing

Nichols' lawyer argued that the FBI may have deliberately withheld information during the course of the trial

Nichols also claimed to have found at least two instances in which the prosecution argued points in court that are contradicted by the new information.

However the US Justice Department replied that nothing in the documents would have helped Nichols, and that their discovery was not sufficient reason to reopen the case.

The Supreme Court had already rejected an appeal from Nichols when the document problem first became public in May.

State trial

Nichols is already facing another possible trial and a death sentence in Oklahoma state court for his part in the bombing.

In the original trial Nichols was convicted on federal charges because eight of those he and McVeigh killed were federal employees.

But Oklahoma County District Attorney Wes Lane is pressing charges of first-degree murder against Nichols for the murder of the other 160 victims.

Mr Lane said he was pursuing the case in part as an insurance policy in case Nichols somehow won an appeal on his federal case.