AUGUSTA — A North Carolina company that agreed to preserve a historic arsenal in Augusta has failed to do so and could be sued if doesn’t take steps by Oct. 1 to prevent further damage, the Maine attorney general’s office said.

In a letter dated Wednesday, the office told a company official that the firm has breached agreements to protect the Kennebec Arsenal, a National Historic Landmark, from vandals, thieves and weather.

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The property, located in downtown Augusta across the Kennebec River from the State House, is considered the best surviving example of a 19th century military complex of its kind. Its eight granite structures, dating back to 1828, were supposed to be renovated for residential and commercial use after the property was conveyed from the state to Main Street I LLC in 2007.

But since then, windows have been smashed and buildings have been broken into and marked with graffiti. Thieves have ripped out copper piping and iron balusters and railings, doors have been broken and fires have been started.

The letter’s recipient, Thomas Niemann, did not answer the state’s assertions directly. But he said Thursday that Main Street bought the property for $280,000 with future payment of $450,000 when building permits are issued for new construction there.

He told the Kennebec Journal in the spring that his Durham, N.C.-based firm is dedicated to its plan for restoring and renovating the complex, but plans have been hampered by the struggling economy.

The attorney general’s letter to Niemann says the state would be open to a “mutually acceptable resolution” in which the 41-acre property would be conveyed back to the state and Main Street would compensate the state for damage to the property.