US Secretary of State Marco Rubio is hosting an international summit in Washington on Thursday that aims to address the threat of "far-left political terrorism".
The administration of President Donald Trump says countries around the world have a blind spot for what US officials see as a rising wave of left-wing political violence.
Mr Trump has clamped down on left-wing groups, particularly Antifa, and has proclaimed that the decentralised anti-fascist movement is a domestic terrorist organisation. Antifa has frequently protested against his hardline immigration enforcement.
Mr Trump has also blamed left-wing extremism for the killing of conservative activist Charlie Kirk in Utah last year.
At least 65 countries have been invited to attend Thursday's day-long event. A senior State Department official told reporters that some interior or foreign ministers would be among those attending.
The summit would help counter-terrorism officials to discuss what the Trump administration says is a growing and sophisticated global threat, the official said.
"Far-left political terrorism is resurgent, manifesting in violent terrorist acts across the Western Hemisphere, Europe, Asia and beyond," the State Department said in a statement. "These are not isolated incidents. They reflect a deliberate, ideologically motivated strategy to destabilise free societies".
Since November, Washington has designated four European groups – Antifa Ost, the Informal Anarchist Federation/International Revolutionary Front, Armed Proletarian Justice and Revolutionary Class Self-Defence – as Foreign Terrorist Organisations, offering rewards of up to $10 million for information on their financing.
Rights groups, including the American Civil Liberties Union, have warned that the terrorism designations could be used against lawful protest and political opponents rather than genuine security threats.
The Trump administration and Republicans have come under criticism for sometimes remaining quiet about right-wing violence, such as last year's attacks on Minnesota Democratic politicians.
The administration also faces questions about how it decides what constitutes political violence after Mr Trump pardoned the rioters who attacked the US Capitol on January 6, 2021.
