TIM's board on Tuesday was briefed about discussions with KKR while also receiving information about an alternative proposal from rival private equity firm CVC for a stake in TIM's enterprise services business.

The sources said TIM and its advisers had concerns about whether KKR's offer stood after the New York-based fund included a reference to recent market volatility in its latest letter to TIM. KKR declined to comment.

The people said TIM in a letter sent to KKR late on Monday asking to confirm the bid's price had also sought details on the financing of the offer, which amounts to 33 billion euros when including debt, after KKR said it did not plan to make extensive recourse to debt.

TIM and KKR are at odds over the nature of a due diligence analysis the U.S. fund has asked to perform on the group's financial data before making a formal bid, the sources said.

In its letter on Monday TIM asked KKR to confirm its due diligence would only have a confirmatory nature.($1 = 0.9021 euros)

(Reporting by Elvira Pollina and Gianluca Semeraro; editing by Valentina Za)