U.S. securities regulators are weighing civil fraud charges against some credit-rating companies for their role in developing the mortgage-bond deals that helped unleash the financial crisis, according to people familiar with the matter. The Securities and Exchange Commission’s long-running probe into the deals has widened to the major credit-rating firms, including Standard & Poor’s, the people said. The leading ratings companies have been criticized by lawmakers as “key enablers” of the financial meltdown, helping to fuel the $1 trillion Wall Street mortgage-securities machine before the boom ended.