Singer Rihanna pulled out of the Grammy Awards after police announced they were investigating an assault claim against her boyfriend, R&B star Chris Brown. Los Angeles police said Mr Brown, 19, had argued with an unidentified woman on Saturday night, and the fight escalated when they got out of a car. He is currently being interviewed by officers, a police spokeswoman said. They did not identify the woman who had made the complaint against Mr Brown, whose performance was also dropped. Mr Brown, who walked into a police station at 1900 local time on Sunday (0300 GMT on Monday), is being held on $50,000 (£34,000) bail, Associated Press reported. "We have just been informed that Rihanna will not be attending tonight's 51st Annual Grammy Awards. We're sorry she is unable to join us," the Recording Academy said in a brief statement shortly before the ceremony. 'Visible injuries' Police said Mr Brown and the woman got into an argument while sitting in a parked car in the city's Hancock Park neighbourhood. "After stopping his car, Brown and the woman got out and the argument escalated," a Los Angeles Police Department statement said. "The woman suffered visible injuries and identified Brown as her attacker." Police received an emergency call reporting the disturbance but when officers arrived, Mr Brown had left the scene. Rihanna was due to sing Live Your Life/Disturbia as the second performance of the night at the Staples Center, while Mr Brown was to sing Forever. They were both nominated in the pop collaboration with vocals category, Brown for No Air with American Idol winner Jordin Sparks; and Rihanna for If I Never See Your Face Again with Maroon 5. Mr Brown was also nominated for male R&B vocal performance for Take You Down. Source: BBC