US President Donald Trump said an Afghan man who fled the Taliban was the suspect in the shooting of two National Guard soldiers near the White House, calling it an "act of terror".

The announcement in a brief video message signalled the intertwining of three politically explosive issues – Trump's controversial use of the military at home, immigration and the legacy of the US war in Afghanistan.

The incident, which left two Guard members critically wounded, was "an act of evil, an act of hatred and an act of terror", he said. "It was a crime against our entire nation."

Trump said the man taken into custody after the daylight shooting two blocks from the White House was "a foreigner who entered our country from Afghanistan".

The suspect had arrived in the United States in 2021 "on those infamous flights", he said, referring to the evacuations of Afghans fleeing as the Taliban took over the country in the wake of the US retreat after 20 years of war.

The shocking attack, carried out next to a metro station at a time when the streets and offices of downtown Washington were bustling, also puts a new focus on Trump's controversial militarization of an anti-crime push around the country.

Trump has deployed troops to several cities, all run by Democrats, including Washington, Los Angeles and Memphis. The deployments have prompted multiple law suits and protests from local officials who accuse the Republican of seeking authoritarian powers.

Trump's statement also indicated that his equally controversial drive to root out migrants in the country illegally – the core of his domestic agenda – will get new impetus.

"We must now reexamine every single alien who has entered our country from Afghanistan" under former president Joe Biden, said Trump.

"We must take all necessary measures to endure the removal of any alien from any country who does not belong here, or add benefit to our country if they can't love our country, we don't want them."

The Operation Allies Welcome initiative brought roughly 76,000 people to the United States, many of whom had worked alongside US troops and diplomats as interpreters and translators.

It has since faced intense scrutiny from Trump and his allies, congressional Republicans and some government watchdogs over gaps in the vetting process and the speed of admissions, even as advocates say it offered a lifeline to people at risk of Taliban reprisals.

The suspect, who has been living in Washington state, has been identified by law enforcement officials as Rahmanullah Lakanwal, but authorities were still working to fully confirm his background, said two law enforcement officials and a person familiar with the matter said.

US officials said processing of all immigration requests relating to Afghan nationals is stopped indefinitely pending further review of security and vetting protocols. (Agencies)