John Malkovich's hotel room in Prague was recently burgled and thieves made off with two cell phones and several documents, reports say.
Representatives for the 57-year-old actor had no immediate comment.
"We can confirm than an investigation is under way in the case of the disappearance of Mr. Malkovich's personal belongings," a spokeswoman for the Mandarin Oriental hotel told the Reuters news wire.
Malkovich had performed in the criminal melodrama "Infernal Comedy," which is based on an Austrian serial killer, at the Prague Spring International Music Festival on Thursday, June 2.
The Czech Republic-based website www.idnes.cz said two cell phones were stolen from the actor's room, while another local website, ceskenoviny.cz, quoted the Polish PAP news agency as saying that several of Malkovich's documents were taken. It said he had new ones issued and postponed a flight to Poland by a few hours.
He was due to fly to the country on Friday to meet with students of the Lodz Film School and perform in a local production of "Infernal Comedy" the next day.
Malkovich is known for films such as "Being John Malkovich," the spy comedy "Red" and recently, "Transformers: Dark of the Moon," the third film in the movie series that is set for release on June 29.