WASHINGTON (AFP) - President Barack Obama expressed joy on Saturday over the release of two Americans who had been held in North Korea, calling their liberation "wonderful."

"I think it is a wonderful day for them and their families and obviously we are very grateful for their safe return, he said at a White House ceremony held to announce the naming of his new attorney-general, Loretta Lynch.

The US State Department earlier on Saturday announced the release of Kenneth Bae and Matthew Todd Miller, and said the two Americans were freed with the help of director of national intelligence James Clapper, who travelled to North Korea to obtain their freedom.

"I appreciate the director doing a great job on what was obviously a challenging mission," Obama said.