The brazen daytime shooting of two National Guard members in the US federal capital by a man authorities said is an Afghan national has raised multiple questions.

That includes the condition of the wounded troops and details about the suspect and his motive for the attack a day before the Thanksgiving holiday.

The United States is treating the shooting as a terrorism investigation, FBI Director Kash Patel said Thursday.

"It is an ongoing investigation of terrorism," Patel told a news conference a day after the incident.

Here’s what we know so far, and what we don’t know:

US Attorney Jeanine Pirro on Thursday identified the two National Guard members who were shot in Washington DC as 20-year-old Sarah Beckstrom and 24-year-old Andrew Wolfe, adding they had undergone surgery and remained in critical condition.

"A lone gunman opened fire without provocation, ambush style, armed with a 357 Smith and Wesson revolver," she told reporters.

Beckstrom and Wolfe belong to the West Virginia National Guard, which deployed hundreds of troops to the nation's capital as part of President Donald Trump's crime-fighting mission that involved taking over the local police department.

There were nearly 2,200 Guard members in DC for the mission.

West Virginia Governor Patrick Morrisey initially posted on social media that two of his state’s Guard members were killed. He later walked that back, saying his office was “receiving conflicting reports” about their condition. Morrisey has not elaborated.

Bowser called the attack a “targeted shooting”.

Jeffery Carroll, an executive assistant DC police chief, said video reviewed by investigators showed the assailant “came around the corner” and immediately started firing at the troops. The suspect opened fire with a revolver, according to a law enforcement official.

At least one Guard member exchanged gunfire with the shooter, another law enforcement official said. Both were not authorised to discuss the matter publicly and spoke on condition of anonymity.

Troops ran over and held down the shooter, Carroll said, and he was taken into custody. Authorities believe he was the only gunman.

Carroll said that it was not clear whether one of the Guard members or a law enforcement officer shot the suspect and that investigators so far had no information on a motive.

The suspect’s wounds were not believed to be life-threatening, one of the officials said.

The suspect is believed to be a 29-year-old Afghan national who entered the US in September 2021 and has been living in Washington state, two law enforcement officials and a person familiar with the matter said.

Law enforcement identified the suspect as Rahmanullah Lakanwal, but authorities were still working to fully confirm his background, they said.

He came to the US through Operation Allies Welcome, a Biden administration program that evacuated and resettled tens of thousands of Afghans after the chaotic US withdrawal from the country, officials said.

NBC and Fox News said Lakanwal had served in the Afghan army for 10 years supporting US Special Forces troops, citing intelligence sources.

FBI's Patel confirmed the suspected shooter had worked in Afghanistan with partner forces.

"We are fully investigating that aspect of his background as well to include any known associates that are either overseas or here in the United States of America, that is what a broad based international terrorism investigation looks like," Patel said at a news conference.

Lakamal arrived in Bellingham, Washington, about four years ago with his wife and five children, according to his former landlord Kristina Widman.

They were among about 800 Afghan refugees that settled in Washington state under Operation Allies Welcome with the financial support of the US government. Among those that partnered with federal agencies to sponsor the Afghan families was World Relief, a faith-based group that helped the refugees with finding housing, employment training and language classes as they settled in the Seattle area.

It's unclear how Lakanwal might have traveled to the nation's capital, which is about 2,500 miles (4,000 kilometres) away.

Trump described Wednesday's “heinous assault” as proof that lax migration policies are “the single greatest national security threat facing our nation".

“No country can tolerate such a risk to our very survival,” he said.

Soon after the shooting, Trump said he would send 500 more National Guard troops to Washington, DC. It's not clear where the additional troops would come from.

As of early November, the DC National Guard had the largest number on the ground with 949. In addition to West Virginia, Louisiana, Mississippi, Ohio, South Carolina, Georgia and Alabama also had forces in the capital early this month.

A federal judge last week ordered an end to the Guard deployment but also put her order on hold for 21 days to allow the Trump administration time to either remove the troops or appeal.