(New throughout)

NEW YORK, April 28 (Reuters) - Thornburg Mortgage Inc (TMA.N: Quote, Profile, Research) said on Monday the U.S. Securities and Exchange Commission has opened a probe into matters related to the "jumbo" mortgage lender's near collapse last month.

In a regulatory filing, Thornburg said it is cooperating with an SEC notice dated April 4 into its restatement of 2007 financial results; real and threatened demands for more collateral from its own lenders and related disclosures; and the valuation of and disclosures concerning its accounting for mortgage-backed securities addressed in the restatement.

Thornburg said the SEC notice indicated the agency has not determined that any securities law violations have occurred.

SEC spokesman John Heine declined to comment.

Separately, Santa Fe, New Mexico-based Thornburg said it is cooperating with a New York Stock Exchange review into trading in its stock prior to Jan 9, when it said unsettled mortgage market conditions were affecting book value. It said the NYSE notice was dated March 6.

Thornburg specializes in mortgages above $417,000, which have typically gone to buyers of more expensive homes who have good credit. It proved vulnerable to tightening credit markets as investors stopped buying those home loans.

The company narrowly avoided bankruptcy after raising $1.35 billion in March from investors including MatlinPatterson Global Advisers LLC, which invests in distressed companies. It said at the time the capital-raising would leave existing shareholders with just a 5.5 percent stake in the company.

Thornburg shares fell four cents in extended trading after the SEC probe was announced. The stock had closed up 5 cents at $1.29 in regular trading Monday on the New York Stock Exchange. (Reporting by Jonathan Stempel; Additional reporting by Rachelle Younglai; Editing by Tim Dobbyn)