WASHINGTON - US President Barack Obama on Monday directed that US flags be flown at half-staff for the funeral of astronaut Neil Armstrong, the first man to walk on the moon.

According to a proclamation issued by the White House, Obama ordered that US flags shall be flown at half-staff at the White House, and all public buildings and grounds, as well as all military posts, naval stations and vessels throughout the day when the legendary astronaut is buried.

The arrangement was "a mark of respect for the memory of Neil Armstrong," said Obama in the proclamation.

The order came two days after the former astronaut's family announced last Saturday that he died at age 82.

Obama on Saturday lamented the death of Armstrong, calling him a man "among the greatest of American heroes -- not just of his time, but of all time."

Armstrong, an iconic space explorer, commanded the Apollo 11 spacecraft that landed on the moon on July 20, 1969 and has been best remembered by saying "That 's one small step for (a) man, one giant leap for mankind."

Armstrong and his fellow astronaut Buzz Aldrin spent two and a half hours walking on the moon, collecting samples, conducting experiments and taking photographs, while astronaut Michael Collins remained in orbit in the command module.