The gathering storm between Apple and some US television studios is becoming more partisan.

NBC Universal refused to sign a new distribution contract with Apple earlier this month, and this week announced plans to offer limited free downloads of shows, such as Heroes and The Office through its own NBC Direct download service.

The move is seen as reflective of NBC's determination to compete with its former online TV show distribution partner. The free shows will only be available to Windows users and will contain embedded advertising.

In the other corner, Fox and CBS have decided to broaden their relationship with iTunes. Both networks are offering season premieres through Apple's service in the US for free.

Fox is offering the season premiere of Prison Break for free download through the service, and plans to follow this up by offering the premier show of new series, K-Ville, a police drama set in post-Katrina New Orleans, for free download through iTunes.

CBS plans to make the series premiere of The Big Bang Theory sitcom availblae for free download through the store.