WASHINGTON — President Barack Obama and first lady Michelle Obama spent a portion of Tuesday at Arlington National Cemetery visiting the graves of service members killed in Afghanistan and Iraq.

The visit to the burial ground across the Potomac River from the White House is part of the president’s observance of the 11th anniversary of the 9/11 terrorist attacks.

The Obamas quietly walked between rows of graves at Section 60, which contains the remains of the most recent war dead. Pausing at several graves, Obama placed presidential “challenge” coins at the base of the headstones. The first headstone listed the names of 10 victims of an Oct. 26, 2009, helicopter crash in Afghanistan.

Earlier, the Obamas placed a wreath at the Pentagon and observed a moment of silence on the White House South Lawn.

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