Washington, July 21 (DPA) US President Barack Obama welcomed the crew of Apollo 11 to the White House Monday to mark the 40th anniversary of their journey to the moon and called the three men 'genuine American heroes.'

On July 20, 1969, Neil Armstrong and Buzz Aldrin were the first humans to set foot on the lunar surface, while fellow crew member Michael Collins circled the moon in the command vehicle.

'I think that all of us recall the moment in which mankind finally was untethered from this planet and was able to explore the stars; the moment in which we had one of our own step on the moon and leave that imprint that is there to this day,' Obama said.

'And it's because of the heroism, the calm under pressure, the grace with which these three gentlemen operated, but also the entire NASA family that was able to, at great risk oftentimes, and with great danger, was somehow able to lift our sights, not just here in the United States but around the world.