WASHINGTON — US President Barack Obama Monday ordered that all official US flags be lowered to half mast to mark the funeral of Neil Armstrong, the astronaut who planted the Stars and Stripes on the Moon.

Obama issued a proclamation to honor Armstrong, who died on Saturday aged 82, and was the first man to walk on the Moon, delivering the immortal line "that's one small step for man, one giant leap for mankind."

The president's order applies to US flags on the top of the White House, all public buildings, military posts, naval stations and US naval ships at sea anywhere in the world, as well as at American embassies and consulates.

The Cleveland Plain Dealer newspaper reported that Armstrong's funeral would be a private affair and would take place on Friday in Cincinnati, Ohio, and that the state's Republican senator Rob Portman will deliver the eulogy.

Earlier, a Republican congressman from Ohio, Armstrong's home state, called on Obama to hold a state funeral for the revered astronaut.

"The letter is simply going to say that we urge the president to declare a state funeral for Neil Armstrong, who is not only a national hero but a world hero," Republican Representative Bill Johnson told AFP.

Armstrong became a world hero when he set foot on the moon on July 20, 1969.

"If that's not worthy of national and world recognition, I don't know what is," Johnson said.

State funerals are elaborate Washington affairs steeped in tradition and history, and mostly reserved for sitting or former US presidents.

The last time a non-president was honored with a state funeral was in 1964, for US Army general Douglas MacArthur.

Obama paid fulsome tribute to Armstrong, an intensely private man, in a written statement on Saturday.

"Neil was among the greatest of American heroes -- not just of his time, but of all time. When he and his fellow crew members lifted off aboard Apollo 11 in 1969, they carried with them the aspirations of an entire nation.

"When Neil stepped foot on the surface of the moon for the first time, he delivered a moment of human achievement that will never be forgotten."

Obama also said that Armstrong's influence would continue to be felt in all those who are dedicated to exploring the unknown.

"That legacy will endure -- sparked by a man who taught us the enormous power of one small step," he said.

Armstrong's family praised him as a "reluctant American hero," saying they hoped his legacy would encourage young people "to be willing to explore and push the limits and to selflessly serve a cause greater than themselves."

The lunar pioneer was decorated by 17 countries and received a slew of US honors, but was never comfortable with his fame and shied away from the limelight.

In a rare television interview in 2005, Armstrong said he did not deserve the attention he received for being the first man on the moon, just steps ahead of fellow Apollo 11 astronaut Edwin "Buzz" Aldrin.