US authorities have seized artworks by the Austrian artist Egon Schiele from American museums following a claim they were looted during the Holocaust.
Investigators in New York have seized three pieces from galleries in Chicago, Pittsburgh and Ohio.
The pictures are being sought by the heirs of Fritz Grünbaum, an Austrian-Jewish art collector, cabaret performer and outspoken critic of Nazism.
The museums say they are confident in their legal ownership of the art works.
Mr Grünbaum, who died in a concentration camp at Dachau in 1941, owned 81 pieces by Schiele.
They were part of a wider collection of more than 400 works of art, according to legal documents from a previous case.
They state that Mr Grünbaum was forced by the Nazis to sign over power of attorney to his wife while he was in a concentration camp in around 1938. The artworks he owned were subsequently, according to documents, looted and dispersed.
The Art Institute of Chicago has confirmed to the BBC that the Manhattan District Attorney's Office seized a painting called Russian War Prisoner by Schiele. It is valued at around $1.25m (£1m).
"We are confident in our legal acquisition and lawful possession of this work," said a spokeswoman for the Art Institute. "The piece is the subject of civil litigation in federal court, where this dispute is being properly litigated and where we are also defending our legal ownership."
The painting was seized "in place" which means it remains in possession of the Art Institute for now. However, warrants seen by the BBC state that it can be moved to New York after 60 days.
A drawing entitled Portrait of a Man has been seized from the Carnegie Museums of Pittsburgh. A warrant states it is valued at $1m.
A spokesman for the Carnegie Museums said they were "deeply committed to our mission of preserving the resources of art and science by acting in accordance with ethical, legal, and professional requirements and norms".
"We will of course co-operate fully with inquiries from the relevant authorities," he said.
A painting called Girl With Black Hair at the Allen Memorial Art Museum at Oberlin College in Ohio has also been targeted. It is valued at $1.5m.
A spokeswoman said: "We are confident that Oberlin College legally acquired Egon Schiele's Girl with Black Hair in 1958, and that we lawfully possess it."
She said the college was "co-operating with the Manhattan District Attorney's criminal investigation".
But she added: "We believe that Oberlin is not the target of the Manhattan DA's criminal investigation into this matter. Per the search warrant, the artwork has officially been seized, and Oberlin is holding it on behalf of the New York court that issued the warrant."
In the warrants, the New York state supreme court states that "there is reasonable cause to believe" the artworks constitute stolen property.
The Manhattan district attorney's office declined to comment,
The living heirs to Mr Grünbaum have been pursuing Schiele works of art for years.
Mr Grünbaum's heirs, who include Timothy Reif and David Frankel, have had some success in securing Schiele paintings.
In 2015, they sued Richard Nagy, a London-based art dealer, and some years later won back Woman in a Black Pinafore and Woman Hiding Her Face.
Mr Nagy appealed against the decision but it was subsequently upheld by the New York Court of Appeals.