The blaze that tore through the landmark Upper East Side townhouse was caused by faulty wiring, FDNY officials announced Monday.

The cause of the two-alarm fire was “accidental, electrical wiring,” according to a tweet posted by the FDNY.

The flames broke out just after 8 p.m. Sunday on the third floor of the Gilded Age mansion at 854 Fifth Ave., which also houses Serbia’s Permanent Mission to the United Nations.

No smoke alarms were present, according to the tweet.

At least five people, including two firefighters, suffered minor injuries. The victims were taken to Lenox Hill Hospital.