HANOI (Reuters) - Vietnamese police issued an arrest order on Friday for a former top Communist Party official suspected of misconduct while he was chairman of the main state energy firm, the first former politburo member to face prosecution in decades.

Police issued arrest and prosecution orders for Dinh La Thang, 56, for suspected “violation of state regulations on economic management, causing serious consequences”, the government said on its website.

Thang is the most senior official to be caught up in a widespread crackdown on fraud in the energy and banking sectors, which has gathered pace since changes in the ruling party leadership early last year.

Police are investigating two cases related to his tenure as chairman of state oil and gas firm PetroVietnam that involved a loss of investment in a domestic bank and suspected wrongdoing at a PetroVietnam subsidiary, PetroVietnam Construction Joint Stock Corp, the government said.

Thang was not available for comment and his whereabouts were not known.

The National Assembly expelled Thang as a lawmaker earlier on Friday, and the Communist Party suspended him from its activities, the government said.

In May, the Communist Party dismissed Thang from the politburo after finding him responsible for financial losses at PetroVietnam.

It also stripped him of his role as party head of Ho Chi Minh City to penalize him further for misconduct during his time as head of the firm.

Prosecuting a former politburo member in the one-party state is not unprecedented. In 1979, a former politburo official, Hoang Van Hoan, was handed a death sentence in absentia after he had fled the country.