GUANTANAMO BAY U.S. NAVAL BASE, Cuba (Reuters) - A potential mistrial was avoided in the first Guantanamo trial on Tuesday when the U.S. military judge ruled it was too late to challenge his war crimes instructions to the jury deliberating the case of Osama bin Laden’s driver.

A photograph of a sketch by courtroom artist Janet Hamlin, reviewed by the U.S. military, shows defendant Salim Hamdan (L) sitting with his defense team during testimony on day three of his trial inside the war crimes courthouse at Camp Justice, the legal complex of the U.S. Military Commissions, at Guantanamo Bay U.S. Naval Base, in Cuba, July 23, 2008. REUTERS/Janet Hamlin/Pool

But the judge acknowledged he may have erred and prosecutors sought clarification on the law that they said could affect plans to try up to 80 more Guantanamo prisoners.

Jurors began deliberating on Monday in the case of Yemeni prisoner Salim Hamdan, who is charged with conspiring with al Qaeda and providing material support for terrorism while working as the al Qaeda leader’s driver in Afghanistan from 1996 until his capture November 2001.

Hamdan was allowed an hour-long phone call with his wife in Yemen on Monday evening, a Guantanamo official said. Defense attorneys said they tried to get permission for her to attend the trial but were refused on grounds that she is married to a terrorism suspect.

Jurors recessed for the night without reaching a verdict on Tuesday.

While they deliberated, prosecutors said the judge had given them flawed instructions on what constitutes a war crime and asked him to call them in for revised instructions.

Defense lawyers said the instructions were correct and that if the judge found otherwise, a mistrial should be declared. They said changing the instructions after deliberations began would be extremely prejudicial to Hamdan, who could face life in prison if convicted.

“It may be that the instruction was erroneous but I guess you’ve waived the right to challenge it by not challenging it sooner,” ruled the judge, Navy Capt. Keith Allred.

Hamdan’s trial is the first in the tribunals the Bush administration created to prosecute non-U.S. citizens on terrorism charges outside the civilian and military court system. The court itself is as much on trial as Hamdan.

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Pentagon spokesman Geoff Morrell called the trial “a good first effort” and said, “We think that you’ve seen a fair and transparent process.”

Military defense lawyers and human rights monitors say the trials are rigged to convict because they allow hearsay and coerced testimony obtained without prisoners being warned that their confessions could be used against them.

“This trial was a betrayal of American values and will rightly be seen as illegitimate by the rest of the world,” said Ben Wizner, who is monitoring the trial for the American Civil Liberties Union.

Prosecutors agreed to withdraw their objections to Allred’s jury instructions rather than risk a mistrial. But they sought clarification on the circumstances under which killing or trying to kill U.S. soldiers is considered a war crime since the issue will arise in other Guantanamo cases.

“We plan on charging at least 80 individuals down here,” said prosecutor Clayton Trivett.

The United States classifies Hamdan and the other 265 Guantanamo captives as “unlawful enemy combatants” who do not fight for a national army or wear uniforms or bear arms openly.

The conspiracy charge accuses Hamdan of agreeing with al Qaeda to commit murder in violation of the laws of war by transporting two surface-to-air missiles that were to be used against U.S. and allied forces in Afghanistan.

In order to find him guilty on that charge, the judge instructed jurors, they must find the missiles were intended for use against protected people -- civilians not involved in hostilities, soldiers removed from combat by illness or capture, or religious or medical personnel.

The prosecution presented no evidence any such people were targeted. They argued the missiles were intended for use against U.S. forces, who had the only planes in the area.

The prosecution wanted the judge to revise the instructions and tell jurors that any attempt by an “unlawful enemy combatant” to kill a U.S. soldier in combat is a war crime.

The defense said that was not the law of war in effect when the alleged acts occurred, and Congress could not retroactively change it in the 2006 law underpinning the Guantanamo trials.

If that had been the law, defense attorney Joe McMillan argued, then the United States committed a war crime by providing missiles to mujahideen forces who used them against the Soviet military in Afghanistan in the 1990s.