Threats against Madonna in Moscow

Russian authorities are stepping up security after a threat of violence at Madonna concerts this week, the U.S. Embassy in Moscow warned.

"The U.S. Consulate General in St. Petersburg has received information regarding a threat of physical violence against spectators and performers at the St. Petersburg concert on August 9," the embassy said in a statement Tuesday.

State Department officials did not provide details about the reported threat targeting Madonna's Thursday show.

"U.S. citizens are reminded to remain vigilant regarding their personal security, and to be aware of their surroundings at all times, especially in crowded areas," the embassy said.

Madonna's spokeswoman Liz Rosenberg said the singer was aware of the threat and the embassy's warning.

"Concerts are going on as scheduled," Rosenberg said.

Madonna performed Tuesday night at a packed Moscow stadium, where she expressed her support for the Russian female punk rock band Pussy Riot, whose members face up to seven years in prison for performing a song critical of Russian President Vladimir Putin.

Madonna said she was praying for the three band members, who went on trial Monday charged with hooliganism, the state-run RIA Novosti news agency reported.

-CNN