New York Attorney General Andrew Cuomo's office has sent letters to Morgan Stanley, JPMorgan Chase & Co., and Wachovia Corp. demanding that they come to the negotiating table as an investigation of sales and marketing of auction-rate securities focuses on "the next group of market participants."

The letters were sent a few days after UBS AG, Citigroup Inc., and Merrill Lynch & Co. Inc., facing mounting pressure from regulators, agreed to buy back more than $36 billion of the securities from customers.

The letters call on Morgan Stanley, Wachovia, and JPMorgan Chase to "enter into immediate talks about resolving the investigation."

Any resolution would need to resemble the settlements that companies reached last week with Mr. Cuomo, other state regulators, and the Securities and Exchange Commission, the letters said.

It was not immediately clear how much clients of JPMorgan Chase, Wachovia, and Morgan Stanley hold in the securities, according to the letters.

UBS agreed last week to buy back nearly $19 billion of auction-rate securities. Citi agreed to buy back $7.3 billion.

Mr. Cuomo's office had accused UBS of civil fraud in its sales and marketing of the securities.

Massachusetts securities regulators had leveled similar accusations against Merrill and UBS.

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