A military judge denied a request Wednesday by defense lawyers for immediate access to the admitted mastermind of the Sept. 11 attacks and two other top imprisoned terrorism suspects.

The attorneys had sought to derail the latest effort to prosecute a driver for Osama bin Laden before a military tribunal at this isolated tropical outpost, but the judge, Navy Capt. Keith Allred, turned them down, citing "security obstacles."

The defense hoped to have Khalid Sheikh Mohammed and two other so-called "high value" detainees at Guantanamo testify to show their client, Salim Ahmed Hamdan, was not a hardcore member of al-Qaida and should not be prosecuted under the U.S. military tribunal system, said Charles Swift, one of the lawyers.

Their goal, Swift told the court, was to interview the people with the "absolute knowledge" of al-Qaida operations.

"We are seeking the detainees who basically would know," he said.

The main military prosecutor, Army Lt. Col. William Britt, argued that the high-value detainees are held under such tight security that he has never spoken to any of them and the defense would have to secure special security clearances.

Allred said he would allow the defense to have access to another Guantanamo detainee, a Moroccan who was captured in Afghanistan with Hamdan.

Hamdan, a Yemeni, has been charged with conspiracy and supporting terrorism.

The developments came as the U.S. Supreme Court met to consider the broad rights of Guantanamo prisoners. The Supreme Court showdown revolves around whether Guantanamo prisoners can challenge their detention in U.S. civilian courts.

A legal challenge by Hamdan prompted the Supreme Court last year to throw out the previous rules for military tribunals.

Air Force Brig. Gen. Thomas Hartmann, the legal adviser to the military tribunal system, said the timing of the hearings in Guantanamo and Washington was coincidental.

The U.S. holds about 305 prisoners on suspicion of terrorism or links to al-Qaida and the Taliban at Guantanamo and plans to prosecute at least 80, including the alleged architect of the Sept. 11 attacks. So far, only three detainees have been formally charged and one, Australian David Hicks, was convicted in a plea bargain and sent home.