U.S. prosecutors stepped up the pressure on Bernard Madoff's family on Tuesday, signaling their intent to ask for $31.5 million from loans to his sons and $2.6 million worth of his wife's jewelry.

Documents filed in U.S. District Court in Manhattan follow a government notice of intent to seek forfeiture this week after Madoff pleaded guilty on March 12 to running the biggest investment fraud in Wall Street history, involving as much as $65 billion over 20 years.

Madoff is the only person charged in the fraud surrounding the family-run business, Bernard L. Madoff Investment Securities LLC, in New York.

Tuesday's notice said that any and all ownership interest held in the name of Ruth Madoff or Bernard Madoff in 20 entities or their subsidiaries is subject to forfeiture.

The notice listed various pieces of jewelry owned or held in the name of Ruth Madoff valued at approximately $2,624,340, and approximately 35 sets of watches and cufflinks owned by Bernard Madoff.

Madoff was jailed after his guilty plea and could face the rest of his life in prison when sentenced in June.

Prosecutors have said they are seeking $170 billion in forfeiture -- everything they can trace back to the fraud, but the figure has been challenged by Madoff's lawyers.

The earlier notice said that prosecutors wanted Madoff and his wife to forfeit more than $100 million worth of homes, cars, boats, securities, silverware and a piano.

The latest notice went further by saying the government sought any and all promissory notes executed by Andrew Madoff and/or Mark Madoff, Madoff's sons, as borrowers in favor of their parents. The notes are due in 2010 or 2012.

The seven loans amounted to $31.5 million dated between March 1, 2004 and October 6, 2008.

Madoff confessed to running a ponzi scheme that bilked thousands of investors. In such a scheme, early investors are paid with money from new ones.

The 70-year-old Madoff pleaded guilty to 11 criminal charges and admitted to defrauding large and small investors and charities in many countries.

(Reporting by Grant McCool; Editing by Toni Reinhold)