Pakistan's top investigative agency has opened an inquiry against former prime minister Imran Khan over allegations that an expensive necklace received as a gift during his tenure was sold to a jeweller for Rs 18 crore instead of depositing it to the state gift repository, according to media report on Wednesday.

The necklace Khan received as a gift was not sent to the tosha-khana (state gift repository), but given to former special assistant Zulfikar Bukhari, who sold it to a jeweller in Lahore for Rs 18 crore, the Express Tribune newspaper reported.

The Federal Investigation Agency (FIA) has initiated a probe against Khan over allegations that an expensive necklace received as a gift during his tenure was sold to a jeweller for Rs 18 crore rather than depositing it to the state gift repository, the report said.

The public gifts can be kept in the personal closet by paying half price of it but Khan, who lost a no-trust vote in Parliament last week, deposited a few hundred thousand rupees in the national exchequer which was illegal, the report said.

According to the law, state officials are required to submit the gifts they receive from dignitaries in the tosha-khana. If they fail to submit the gift or at least half the amount the gift is worth, it is an illegal act.