(Reuters) - AT&T Inc is no longer an official sponsor of Fox's American Idol, as the pioneer singing competition's declining viewership appears to be making it less attractive to advertisers.

The Fox broadcast TV network confirmed the end of AT&T's sponsorship on Wednesday prior to the premiere episode of the show's 13th season.

AT&T could not be immediately reached for comment outside regular U.S. business hours.

Coke and Ford also sponsor the show.

Idol erupted in 2001 as a broadcast TV powerhouse with the biting commentary of one of its original judges, Simon Cowell. Last season, tension between judges Mariah Carey and Nicki Minaj made headlines, taking attention away from the talent.

According to Nielsen data provided by Horizon Media, the average audience size for Idol dropped by 9.9 million viewers over the past three seasons, from 23.1 million in 2011 to 13.2 million last year.

Kevin Reilly, chairman of entertainment for Fox Broadcasting Company, had said Idol viewership will likely slip again this season - a typical scenario for aging reality shows.

Declining ratings has been a drag on advertising revenue at the Fox broadcast network's parent 21st Century Fox, the company reported in August.

Tags: American Idol