(Reuters) - The Justice Department has stepped up its investigation of Standard & Poor's mortgage bond ratings during the financial crisis, the Wall Street Journal reported on Tuesday.

At least five former S&P analysts have been contacted by federal prosecutors in recent weeks, after some had not heard from investigators for more than six months, the newspaper said.

The McGraw-Hill Cos Inc unit disclosed in September it had received a Wells notice from the Securities and Exchange Commission indicating it could face civil charges for its ratings of a 2007 mortgage bond deal called Delphinus 2007-1.

It has not yet disclosed any investigation by the DOJ, which the WSJ reported is a civil probe.

Prosecutors are examining whether S&P managers pushed to weaken standards the company had set for rating the mortgage deals, and whether the company followed its established criteria in assigning ratings.

The recent interviews lasted two to three hours, and the former employees were told they would likely by contacted again, the Wall Street Journal said.

A spokesman for S&P declined comment.

(Reporting By Aruna Viswanatha; Editing by Gerald E. McCormick)