Los Angeles, Oct 30 (IANS): Singer Pharrell Williams has warned US President Donald Trump against playing his "Happy" song, after it was used at a rally just hours after the Pittsburgh synagogue shooting.

Williams' attorney Howard E. King sent a cease-and-desist letter to Trump on Monday after "Happy" was played at his Saturday rally in Murphysboro in Illinois, reports variety.com.

"On the day of the mass murder of 11 human beings at the hands of a deranged ‘nationalist', you played his song ‘Happy' to a crowd at a political event in Indiana," King said in the letter.

"There was nothing ‘happy' about the tragedy inflicted upon our country... and no permission was granted for your use of the song...," he added.

Eleven people from the age group of 54 to 97 were gunned down on October 28 at the Tree of Life synagogue, where three separate congregations were holding services.

Gunman Robert Bowers has been charged with 29 counts of federal crimes including murder, ethnic intimidation and hate crimes.

Trump acknowledged the shooting at the Illinois rally as a "wicked act of mass murder", "pure evil, hard to believe and frankly something that is unimaginable".

Williams, however, would still not allow Trump to use any of his music under any circumstances. "Pharrell has not, and will not, grant you permission to publicly perform or otherwise broadcast or disseminate any of his music.

"The use of ‘Happy' without permission constitutes copyright infringement," the legal notice to Trump said.