LONDON (Reuters) - The FTSE 100 endured early weakness on Wednesday, having hit 13-year highs in the previous session, as investors trade cautiously awaiting further clues from the U.S. Federal Reserve over its the outlook for its stimulus measures.

London's blue chip index fell 8.87 points, or 0.1 percent to 6,795.00 at 0710 GMT.

Its close of 6,950.60 on Tuesday was its highest since late 1999, with equities partly driven by the loose central bank monetary policy which has driven down yields in other asset classes.

Despite two senior Fed officials playing down the chances of the central bank signalling a readiness to trim its bond buying programme, some investors remain cautious.

Fed chairman Ben Bernanke is due to testify in front of congress later in the session, while the minutes from the Federal Open Market Committee's April 30-May 1 policy meeting will be released at 1800 GMT.

"Given the chairman's previous emphasis on the employment to population ratio, there would seem little reason for him to hint at any meaningful tapering of purchases this year. Nevertheless that is what the market expects," Guy Foster, head of portfolio strategy at Brewin Dolphin, said.