WASHINGTON (Reuters) - Federal regulators approved Clear Channel Communications Inc.'s $15.5 billion acquisition of AMFM Inc. creating the nation's No. 1 owner of radio stations.

The U.S. Federal Communications Commission said it approved the purchase after the two agreed to sell 23 more stations in 10 markets to either third-party buyers or to an insulated trust in order to satisfy FCC rules on local radio ownership and radio-television cross-ownership.

The U.S. Justice Department, which reviewed potential competition and antitrust concerns, had approved the combination July 20 on the condition that the two companies divest 99 stations in 27 markets.

In total, 122 stations will be sold in 37 markets.

Clear Channel operates 830 radio and 19 television stations in the United States and has equity interests in over 240 radio stations internationally. Its subsidiary, Eller Media, operates more than 550,000 outdoor advertising displays.

Dallas-based AMFM owns 465 stations in the United States, and is also a distributor of radio programming and media software.