US President Barack Obama places a wreath at the Tomb of the Unkowns at Arlington National Cemetery on Memorial Day in Virginia May 26, 2014. [Photo/Agencies]

WASHINGTON - US President Barack Obama paid tribute on Monday to fallen US military men and women during a Memorial Day ceremony at Arlington National Cemetery that highlighted a veterans' care scandal that has engulfed his presidency in recent weeks.

Just hours earlier, Obama returned from a surprise trip to Afghanistan, where he thanked troops for a mission that will conclude formally at the end of this year. The president noted that more had to be done to ensure that those who served in the armed forces abroad were treated well when they came home.

"We rededicate ourselves to our sacred obligations to all who wear America's uniform, and to the families who stand by them always," Obama said, pledging troops would have needed resources and that the United States would continue to search for those who had gone missing or become prisoners of war.

"As we've been reminded in recent days, we must do more to keep faith with our veterans and their families, and ensure they get the care and benefits and opportunities that they've earned and that they deserve," he said.

The Obama administration has been stung by allegations that veterans have suffered long delays in receiving healthcare and that the Department of Veterans Affairs had engaged in mismanagement and cover-ups.

During a press conference last week, Obama indicated Veterans Affairs Secretary Eric Shinseki's job could be on the line if the issues are not fixed. Shinseki was present at the Arlington ceremony but did not speak.

Before his remarks, Obama laid a wreath at the Tomb of the Unknown Soldier, an annual ritual. Taps was played while the crowd of dignitaries and visitors stood silently.

Obama singled out those who had served in Afghanistan, including the men and women he met during a roughly four-hour trip to Bagram Air Base on Sunday.

"Our troops are coming home. By the end of this year, our war in Afghanistan will finally come to end," he said to applause from the crowd.

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