It's better late than never for US President Barack Obama as he finally issued a proclamation on Tuesday afternoon ordering all flags at the White House and other federal buildings in the country to be flown at half-staff to honour the victims of last week's shooting rampage in Chattanooga, Tennessee.

Obama made the move after facing criticism from lawmakers and others who wondered why he did not immediately ordered the lowering of US flags at the White House and other public buildings, which he has done in previous tragedies.

Congressional leaders ordered flags at the US Capitol lowered to half-staff earlier on Tuesday, sparking questions why the White House hadn't done the same yet.

Rep. Duncan Hunter, R-California, a veteran, earlier released a statement calling it "unconscionable" that the flags had not been lowered, as of Tuesday morning. "The flag and all it represents is sacred to our military, and the President must know that lowering the flag is a signal of honour and respect," he said.

On Monday, a Marine challenged Americans to "teach Obama respect" by flying all US flags at half-staff in honour of the five service members killed in the deadly Chattanooga attack.

Mike Shepard, who said he served in the US Marine Corps for nine years, issued his challenge on the website DCGazette.com:

"Most are fully aware of the president not showing support for our fallen and flags continue flying high in the sky. He invited the family of a traitor named Berghdal to the rose garden to celebrate the release of our enemy. He has yet to call out the terrorist who shot up two recruiting stations in Chattanooga. Well, we don't need permission to show our respect for those five lives lost. I am reaching out to you America in hopes that we teach Obama about respect.

"I say we should come together and fly our flags at half mast until the 30th of July. The 30th will mark the two week anniversary of this tragedy. Let's show the president what it is to respect this country and our fallen," Shepard wrote.

Rep. Scott DesJarlais, R-Tennessee, joined the critics, telling Fox Business Network that he "can't imagine" why Obama had not ordered the flags be lowered as of Monday. He added that it "needs to happen and it needs to happen soon."

Heeding the mounting calls, President Obama issued the order on Tuesday afternoon ordering that flags be lowered to half-staff at the White House and federal buildings across the country.

Obama said all flags are to be flown at half-staff until July 25 in all US government offices and military posts in the country and overseas.

"Our thoughts and prayers as a nation are with the service members killed last week in Chattanooga," Obama said. "We honour their service. We offer our gratitude to the police officers and first responders who stopped the rampage and saved lives. We draw strength from yet another American community that has come together with an unmistakable message to those who would try and do us harm: We do not give in to fear. You cannot divide us. And you will not change our way of life."

Flags at the US Capitol were ordered flown at half-staff before his order.

The proclamation was issued shortly along with similar orders from Senate Majority Leader Mitch McConnell and House Speaker John Boehner, reports said.

"Last week, five brave service members were murdered in a terror attack in Chattanooga, Tennessee. Out of respect for their courageous service and sacrifice to our nation, flags at the US Capitol are being lowered to half-staff," Boehner said.

It said the House will offer a moment of silence for the victims on Tuesday night.

"[T]he US Senate's thoughts are with their families and loved ones, and with all those who protect us here, and around the world," McConnell said.

A Navy sailor and four Marines were killed in the attack by suspect Mohammad Abdulazeez, who was killed by the police.