WASHINGTON (Reuters) - The Pentagon warned on Thursday in a letter to a former U.S. Navy SEAL that he was in material breach of non-disclosure agreements with his book detailing his first-hand account of the raid that killed Osama bin Laden.

The letter, a copy of which was obtained by Reuters, also said the Pentagon was considering legal action against the SEAL and all those "acting in concert" with him.

"In the judgment of the Department of Defense, you are in material breach and violation of the non-disclosure agreements you signed," the letter by Jeh Johnson, the Pentagon's top lawyer, said. "Further public dissemination of your book will aggravate your breach and violation of your agreements."

(Reporting by Phil Stewart)