By Kristin Roberts

WASHINGTON, June 22 (Reuters) - The Pentagon said on Friday it sent a suspected commander of an al Qaeda-affiliated group to the military prison in Guantanamo Bay, increasing detainee ranks at the facility as some U.S. officials in Washington weigh closing it.

The Pentagon said it transferred Haroon al-Afghani from a U.S. military facility in Afghanistan to the detention center at the U.S. Navy base in Cuba this week.

Al-Afghani was captured in Afghanistan but Pentagon spokesman Bryan Whitman said he did not know when.

According to the Pentagon, al-Afghani admitted serving as a courier for senior al Qaeda leadership.

The Defense Department said al-Afghani also served as a senior commander of Hezb-i-Islami, a group run by Afghan warlord Gulbuddin Hekmatyar and associated with al Qaeda in Afghanistan. It said he commanded cells that used improvised explosive devices, the roadside bombs that have proved deadly to U.S. and coalition troops.

"He is a person with significant knowledge ... and may have additional information with respect to ongoing al Qaeda operations and may have information that is useful to us in thwarting future attacks," Whitman said.

Whitman would not say who had captured al-Afghani.

The United States has faced international criticism over its continued detention of about 375 suspected al Qaeda and Taliban members at the Guantanamo Bay prison.

Human rights groups and other critics have demanded the Bush administration close Guantanamo and that detainees be charged with crimes or released.

U.S. Defense Secretary Robert Gates has suggested Congress explore with the White House ways to close the prison while keeping the most dangerous detainees imprisoned.

Senior administration officials had been scheduled to discuss the issue on Friday but canceled the meeting after news reports that the administration was close to agreement on closing the facility. (Additional reporting by Andrew Gray and Caren Bohan)

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