MILAN (Reuters) - Shares in Mediaset <MS.MI> were lower in early trade after a war of words with France's Vivendi <VIV.PA> over the sale of the Italian broadcaster's pay TV unit escalated.

On Thursday Vivendi said the binding share-swap agreement it signed in April with Mediaset for its Premium pay-TV unit could be void after Sept. 30.

Mediaset immediately replied that Vivendi's statements were devoid of any legal or commercial basis.

But sources said the two groups were negotiating behind closed doors to forge an alternative partnership.

"The talks nonetheless look to be difficult because Premium results are still negative and the two companies don't want the numbers to weigh on their respective balance sheets," Milan broker ICBPI said on Friday.

At 0712 GMT Mediaset shares were down 1.8 percent.

(Reporting by Stephen Jewkes)