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* FTSE 100 down 0.2%, FTSE 250 off 0.3%

Jan 31 (Reuters) - The UK's blue-chip index dipped in early deals on Wednesday, dragged down by Vodafone and GSK, while underwhelming results from major U.S. technology companies and caution ahead of a Federal Reserve policy decision weighed on the global mood.

The blue-chip FTSE 100 dipped 0.2% by 0814 GMT, with Vodafone slipping 2.2% after French telecom operator Iliad said its British peer had rejected its revised proposal to merge their Italian businesses.

Shares of GSK dipped 0.3% even as the drugmaker beat market estimates for fourth-quarter results.

The midcap FTSE 250 shed 0.3%, with Harbour Energy falling nearly 5% after Goldman Sachs downgraded the oil and gas producer's shares to "sell" from "buy".

Both the FTSE indexes were headed for their first monthly decline in three as investors scaled back bets of aggressive interest rate cuts from major central banks, with concerns about China's slowing economy adding to the gloom.

The Fed is widely seen holding interest rates later in the day, with focus on Fed Chair Jerome Powell's post-meeting press conference and any hints from policymakers on how soon the Fed could begin easing rates. (Reporting by Sruthi Shankar in Bengaluru; Editing by Sherry Jacob-Phillips)