The investigation, according to the Financial Times newspaper, will examine whether the Big Four firm breached auditing rules in its work on Fannie Mae.

Fannie Mae is already under investigation by both the Justice Department and the Securities and Exchange Commission.

It faces a $9bn restatement following a Security and exchanges Commission ruling that it had violated accounting rules between 2001 and 2004.

KPMG, which has audited the company for the past 35 years, said it would 'cooperate fully' with any investigation.

The PCAOB is a private sector body created by the Sarbanes-Oxley Act to oversee the auditors of public companies.