Washington DC - President Donald Trump said on Thursday he would suspend migration from what he called "Third World Countries," a day after an Afghan national allegedly shot two National Guard soldiers in Washington, killing one.

His social media post, which also threatened to "denaturalize migrants who undermine domestic tranquility" and reverse "millions" of admissions granted under his predecessor Joe Biden, marked a new escalation in the anti-migration stance.

Trump said earlier that Sarah Beckstrom, a 20-year-old West Virginia National Guard member deployed in Washington, had died from her wounds.

The other soldier wounded in the attack, 24-year-old Andrew Wolfe, was "fighting for his life", Trump said. The suspected shooter, identified as Rahmanullah Lakanwal, was also in serious condition.

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The FBI has launched an international terror investigation as new details emerged about the 29-year-old Afghan national who was a member of the "Zero Units" – a CIA-backed "counterterrorism" group, according to multiple media reports.

"I will permanently pause migration from all Third World Countries to allow the U.S. system to fully recover," Trump wrote on social media.

He linked the shooting and his decision to send hundreds of National Guard troops to the city.

"If they weren't effective, you probably wouldn't have had this done," Trump said. "Maybe this man was upset because he couldn't practice crime."

US Citizenship and Immigration Services said on Thursday it was launching a "full-scale, rigorous reexamination" of green card holders from countries "of concern."

The heads of the FBI, CIA and Homeland Security and other senior Trump appointees all insisted that Lakanwal had been granted unvetted access to the US because of lax asylum policies in the wake of the chaotic final US withdrawal from Afghanistan under former President Joe Biden.

However, AfghanEvac, a group that helped resettle Afghans in the US after the military withdrawal, said they had undergone "some of the most extensive security vetting" of any migrants.

Pentagon chief Pete Hegseth said in the wake of Wednesday's shooting that 500 more troops would deploy to Washington, bringing the total to 2,500, despite a federal judge previously ruling that the deployment is unlawful.