WELLINGTON, New Zealand — The police in New Zealand said on Thursday that they were looking into a claim that a man who said he once worked for Russian intelligence was poisoned in Auckland more than a decade ago.

The man, Boris Karpichkov, who said he worked for the K.G.B. before becoming a double agent and later claiming asylum in Britain, spent 15 months in New Zealand in 2006 and 2007.

Mr. Karpichkov told the British television show “Good Morning Britain” this week that he had powder thrown in his face by someone “dressed as a common beggar” on a busy street in Auckland, New Zealand’s largest city. He said he became ill, losing his hair and more than 65 pounds.

Image Boris Karpichkov appearing on “Good Morning Britain” this week. Credit... Good Morning Britain/ITV

His doctor initially told him he had the flu, Mr. Karpichkov said, and he did not report the episode to the police at the time.