US share prices staged a late rally on Monday after Standard & Poor’s affirmed the top-notch credit ratings of beleaguered bond insurers MBIA and Ambac and said MBIA was no longer at risk of a downgrade.

However, S&P indicated that it could still downgrade Ambac, depending on the outcome of behind-the-scenes talks now being conducted between banks and rating agencies on a $3bn rescue plan for the bond insurer.