The US House ethics panel has extended its investigation into congresswoman Alexandria Ocasio-Cortez over allegations that she may have violated congressional rules.

A nonpartisan watchdog review found "substantial reason to believe that she accepted impermissible gifts" related to a fashion event.

The probe centres on the payments for the dress she rented to attend the prestigious Met Gala in 2021.

The lawmaker has denied any wrongdoing.

In 2021, Ms Ocasio-Cortez made headlines at the New York City's Metropolitan Museum of Art event wearing a white dress with the words "Tax The Rich" scrawled across the back.

The Office of Congressional Ethics (OCE), a nonpartisan watchdog, issued a report on Thursday that says the Democratic politician was provided with the dress, a handbag, shoes and jewellery for the event. She also received hair, makeup and transportation services as well as the use of a hotel room for the event.

"While Rep. Ocasio-Cortez appears to have now paid for the rental value of the attire she wore to the Met Gala and for the goods and services she and her partner received in connection with this September 2021 event, payment for these goods and services did not occur until after the OCE contacted her in connection with this review," the OCE said in a report released on Thursday.

"If Rep. Ocasio-Cortez accepted impermissible gifts, then she may have violated House rules, standards of conduct, and federal law," the OCE report said.

The OCE board recommended in June 2022 that the House review the allegations against Ms Ocasio-Cortez. The House Ethics Committee announced in December that it was investigating her, though it did not disclose the subject of its inquiry at the time.

Ms Ocasio-Cortez's counsel David Mitrani has said the congresswoman "finds these delays (in payment) unacceptable, and she has taken several steps to ensure nothing of this nature will ever happen again."

"However, while regrettable, this matter definitively does not rise to the level of a violation of House Rules or of federal law," he added.