A bar worker at a popular Times Squares karaoke club was arrested yesterday after confessing to beating a woman to death with a pipe on the club’s roof during an argument, police said.

Syed Rahman, 24, admitted he smashed Ingrid Rivera over the head at about 2:45 a.m. Monday during a birthday party for rapper Lil’ Kim that the victim had paid to attend, Police Commissioner Raymond Kelly said at a news conference. Her body was discovered Wednesday afternoon.

It was unclear what Mr. Rahman and Rivera, who had met for the first time inside Spotlight Live club that night, were arguing about. But a friend of Rivera pointed police to Mr. Rahman by telling them she had fought off his sexual advances on the roof shortly before the slaying, Mr. Kelly said.

Charges against Mr. Rahman — who had worked at the club for four years and had no criminal record — were pending. The medical examiner ruled the death a homicide yesterday after an autopsy found that the 24-year-old Rivera died from a blow to the head.

Lil’ Kim’s spokesman, Ronn Torossian, said in an e-mailed statement that Wednesday night was “the first (she) has heard of this matter.”