Ackman says Buffett's offer is positive for markets

NEW YORK (Reuters) - Warren Buffett's offer to reinsure $800 billion of municipal bonds insured by bond insurers is a positive for the capital markets, Bill Ackman, founder of Pershing Square Capital Management, which has sold bond insurer shares short, said on CNBC.

Bond insurers are at risk of losing their top credit ratings, and in some cases already have. Downgrades may force investors in insured bonds to sell their securities, forcing bond prices lower and lifting borrowing costs for cities and consumers.

Reinsurance for the municipal bonds could prevent forced sales, which would be positive for the markets, Ackman said.

(Reporting by Dan Wilchins; Editing by Braden Reddall)