Ukrainian President Volodymyr Zelenskyy's trip to Washington is being treated as a mini state visit – one with extraordinary security implications, according to multiple sources familiar with the plans.
Hundreds of law enforcement and intelligence officials have been activated and the U.S. Secret Service will be the lead agency as he heads to the White House and speaks to Congress Wednesday.
"From the moment he lands and walks down those stairs of his plane, he will have a Secret Service security detail," one official told ABC News.
"He will have that detail until he gets on the plane to leave," the official said.
The Secret Service will provide the vehicles for his motorcade and will be assisted with the motorcade by Prince George's County police and Washington D.C. Metropolitan Police.
Zelenskyy will have his own Ukrainian security detail with him as well.
Don Mihalek, a former United States Secret Service agent told ABC News the Secret Service protects all foreign heads of state while on U.S. soil.
"The Secret Service is responsible for the protection of all visiting foreign heads of state," he said. "They will mobilize a multi-agency security umbrella to ensure his visit is kept safe."
Security officials at the most senior levels of government are "very" concerned about the prospect of something happening during the visit and when he returns home, domestically or abroad, one source told ABC News.
Zelenskyy's trip to Capitol Hill will be similar to State of the Union security preparations because of the high level nature of the address, the official said.
"Being that they are at war with the Russians, not only is there threats potentially from Russian agents, and Russian collaborators, but there will also be threats from those that oppose Ukraine's independence and other nations that might have a vested interest in seeing that Ukraine is not successful," Mihalek, an ABC News contributor said.
According to an email sent to staff at the Capitol and obtained by ABC News, security measures will be "significant." The email says only staff and members will be allowed in the House wing past a certain time.
The Secret Service also is consulting with the Capitol Police, CIA, FBI and other intelligence agencies about the security environment. Every Capitol Police officer will be on standby, according to one law enforcement official.
"We are very cognizant that Russia has assets in this country and might try to do something," one senior official said. "We know what is at stake."
The U.S. is aware that early on in the conflict the Russians apparently plotted to kill Zelenskyy and the official expressed concern that news of Zelensky's visit broke so early about him coming to the United States. It would have been much better, he said, if our adversaries had less time, not more time, to think about doing something and to move assets and operatives around.
The official went on to say he is concerned about Zelensky's security once he leaves the country.
"Putin and the Kremlin know he has to get back to home," the official said.