MILAN (Reuters) -KKR cannot confirm its 10.8 billion euro takeover approach for Telecom Italia (TIM) unless Italy’s biggest telecoms group provides access to the its books, the U.S. fund said in a letter to TIM, according to a source. KKR submitted its non-binding takeover proposal for TIM in November, having already invested 1.8 billion euros for a 37.5% stake in the group’s last-mile fixed-line network. TIM left the New York-based fund waiting for four months without an answer before agreeing earlier in March to engage in talks, while pressing ahead with its standalone reorganisation centere…