New-York based Cablevision Systems will give customers another 15 free high-definition channels as it faces competition from satellite TV providers and Verizon. The cable operator said on Wednesday it would add mainstream HD channels including Discovery, Viacom Inc's Nickelodeon, FX, FOX News, AMC and The Weather Channel to its line-up from July 28, bringing its HD offering to 60 channels.

Cablevision said more than 1.1 million of its digital cable subscribers have at least one high-definition TV and HD-enabled set-top box.

Cablevision, which has more than 3 million subscribers, is keen to fight off competition from satellite rivals DIRECTV Group and DISH Network Corp , as well as a growing threat from Verizon's expanding FiOS TV service.

DIRECTV has said it will have capacity for more than 150 HD channels by the end of this year and currently has 95. DISH has around 80 HD channels.

Verizon, which is in a fierce battle for TV subscribers with Cablevision, currently offers 30 HD channels on its FiOS TV service and said it would add another 30 in the next couple of months.

The phone company said it would also have capacity for 150 HD channels by year-end.