WASHINGTON (AFP) - Michelle Obama took to Twitter on Sunday to send her husband an affectionate birthday message - and a gentle ribbing about the US President's greying hair.

"Happy birthday, Barack! Your hair's a little greyer, but I love you more than ever," Michelle Obama wrote on her official twitter account, @FLOTUS.

The message was accompanied by an undated black and white photo of the Obamas as a young couple relaxing on a sofa.

Barack Obama is spending his 52nd birthday weekend at Camp David, the rural Maryland retreat made available to US Presidents. He was to return to Washington later Sunday.