Washington -- President Donald Trump vowed a wide-ranging crackdown on millions of immigrants in the US as he said an Afghan national was the suspect in the shooting of two members of the National Guard in Washington.

US Citizenship and Immigration Services suspended processing of applications from Afghan nationals after the shooting. They were halted immediately ‘‘pending further review of security and vetting protocols’’, it said on social media.

The president said the suspect in Wednesday’s attack had arrived in the US in 2021, as the Biden administration evacuated tens of thousands of people from Afghanistan during a chaotic US withdrawal after 20 years of war, following which the Taliban returned to power.

In a speech on Wednesday night, Trump called the shooting of two West Virginia National Guard troops near the White House “an act of terror” — and vowed his administration would “re-examine every single alien who has entered our country from Afghanistan”.

Trump described the admission of “unvetted foreigners from all over the world” under the previous administration as the “single greatest national security threat”.

The attack, which took place at about 2.15pm on the day before the Thanksgiving holiday, rattled the US capital and a nation already on edge after a series of high-profile episodes of political violence in recent months.

The targeting of National Guard troops will probably further inflame the controversy around their deployment.

Trump in recent months has ordered National Guard troops into several large, mostly Democratic-led cities, including Washington, in what he says is a campaign to deal with crime and civil unrest. The deployments have prompted legal challenges over the limits to presidential power.

Speaking from West Palm Beach in Florida on Wednesday, Trump vowed “the steepest price” for “the animal who perpetrated this atrocity”.

“He was flown in by the [Joe] Biden administration . . . on those infamous flights that everyone was talking about,” Trump said.

He also attacked his predecessor for admitting people from other nations, claiming that “hundreds of thousands of Somalians” arriving in Minnesota were “ripping apart that once great state”.

Trump directed defence secretary Pete Hegseth to deploy an additional 500 National Guard members to Washington DC.

The shootings took place near the Farragut West metro station, two blocks from the White House in the downtown area of the US capital.

Jeffery Carroll, executive assistant chief of Washington’s Metropolitan Police Department, told reporters the suspected shooter “came around the corner . . . and discharged” at the guardsmen who were patrolling near the White House.

Other troops nearby were able to “hold down the suspect after he had been shot on the ground”, Carroll said. The suspect is now in custody and is being treated at a local hospital.

Muriel Bowser, the mayor of Washington, DC, called the attack “horrific and unconscionable” in a post on X.

She said the suspect “will be prosecuted to the full extent of the law”.

FBI director Kash Patel said the bureau had “assembled the full force” of federal, state and local law enforcement to investigate, and that the attack would be prosecuted as a federal crime.

The shootings near the White House come after a man assassinated conservative activist Charlie Kirk at an event in Utah in September. 

Melissa Hortman, a Democratic state lawmaker in Minnesota, and her husband Mark were murdered in June. The month before that, a shooter killed two Israeli diplomats in Washington.

Last year, Trump survived two assassination attempts during his campaign for the White House.