Nichols has offered to forgo appeals

Nichols has offered to drop appeals against his life sentence - a federal sentence - if the Oklahoma state charges are dropped.

Eight of the people killed in the bombing were federal employees, which is why McVeigh and Nichols were tried on federal charges.

Oklahoma's case concerns the other 160 people killed in the blast, the most deadly militant attack ever on US soil.

Mr Lane, who took over as district attorney on the retirement of Bob Macy in June, had been weighing up how to proceed.

At the very heart of our justice system is the principle of accountability and responsibility

District Attorney Wes Lane

There have been public concerns that pursuing the case would be too expensive. Estimates place the total cost of prosecution and public defence at more than $20m.

But others argue that the state should pursue its case for fear that Nichols might one day be paroled from his federal life sentence.

"At the very heart of our justice system is the principle of accountability and responsibility for those who are alleged to have committed the most serious crimes," Mr Lane said.

"With that in mind, I have decided that the state of Oklahoma will proceed with the prosecution of Terry Nichols."

Appeals

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.

A receipt linked Nichols to the purchase of fertiliser used in explosives

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

But in an unusual move, Nichols' lawyers have now written to an Oklahoma newspaper, offering to drop all appeals if the state dropped its case against their client.

"Taking such a step ensures that he will spend the rest of his life in prison," lawyer Brian Hermanson said in a letter published in the Tulsa World on Wednesday.

"It would enable Mr Lane to drop the state prosecution, thereby sparing Oklahoma the trauma and expense of another trial," the lawyer added.

Mr Lane's office refused to comment on the offer, saying Mr Hermanson had broken a court order by publicising it.

McVeigh admitted his role in the 1995 bombing

Nichols, 46, was sentenced in 1997 for having helped McVeigh, an old army colleague, build the truck bomb which destroyed the Alfred P Murrah building.

He was also found guilty on a second charge of involuntary manslaughter, relating to the deaths of eight federal agents who died in the explosion.

Nichols was acquitted on federal charges of first- and second-degree murder.