Thornburg says had margin calls on mortgage debt Thu Feb 28, 2008 7:33am EST NEW YORK, Feb 28 (Reuters) - Thornburg Mortgage Inc (TMA.N: Quote, Profile, Research), a lender trying to recover from tough credit market conditions, said on Thursday it has been subject to margin calls on about $2.9 billion of mortgage securities following a sudden deterioration in mortgage market conditions. In its annual report filed with the U.S. Securities and Exchange Commission, Thornburg said that since Feb. 14 it has met more than $300 million of margin calls. It said these are tied largely to the declining value of $2.9 billion of "super-senior, credit-enhanced mortgage securities" that carry "triple-A" ratings and are backed by near-prime, "Alt-A" mortgages. It said the market value of the securities has fallen 10 percent to 15 percent this month but it has yet to realize any losses. Thornburg said that because of the market value decline, it has "reduced readily available liquidity" to meet future margin calls. It said if it cannot use cash to meet such calls, it might need to "selectively" sell assets.