KUALA LUMPUR, Malaysia — Malaysian authorities ordered former Prime Minister Mahathir Mohamad's political party to temporarily disband Thursday in a blow to the opposition ahead of an expected general election.

The Registrar of Societies said the Parti Pribumi Bersatu Malaysia failed to submit adequate documentation for its registration and asked it to do so within a month or be permanently deregistered.

Elections are due by August but Prime Minister Najib Razak is widely expected to dissolve Parliament on Friday to pave the way for a vote next month. Support for Najib's ruling coalition has dwindled in the last two elections, and in 2013 it lost the popular vote for the first time.

Mahathir, Asia's longest serving leader for 22 years when he retired in 2003, called Thursday's order "tyranny" and unconstitutional because the party had given all necessary documents to the registrar last week.

Mahathir, 92, said the party will appeal to the home minister, and if that is unsuccessful, it will file a legal suit challenging the order. He said the move was aimed at preventing Pribumi from contesting the election and at blocking the registration of the opposition alliance as a united front.

"We will tell the whole world that the ROS is in breach of the law. There is no rule of law and Najib is cheating to win the elections by terrorizing his opponents," he told a late-night news conference after a party meeting. "Whatever happens to us, we are going to contest ... no way are they going to stop us from contesting."

Mahathir now heads a four-party opposition alliance that has named him as its prime minister candidate. The parties have said they will contest the election under one logo but have not yet successfully registered their alliance. Mahathir said the alliance will make a key announcement Friday on how it plans to contest as a united front.

Pribumi party official Wan Saiful Wan Jan said the registrar's move was "an abuse of power by a regime that is desperate to stay in office."

Angered by an international financial scandal involving the 1MDB state fund set up by Najib in 2009, Mahathir made a high-profile return to politics two years ago in a bid to oust Najib and the ruling coalition that has been in power since independence from Britain in 1957.

Mahathir has helped unite a fractured opposition, which hopes his influence will help it win votes from rural ethnic Malays, the bedrock of support for Najib's government.

The U.S. and several other countries are investigating allegations of cross border embezzlement and money laundering at the fund, which has accumulated billions of dollars in debt. The U.S. Justice Department says at least $4.5 billion was stolen from 1MDB by associates of Najib and it is working to seize $1.7 billion allegedly taken from the fund to buy assets in the U.S.

Najib, who denies any wrongdoing, has fired critics within the government and muzzled the media since the scandal erupted three years ago. Analysts expect Najib to win a third term due to infighting in the opposition, unfavorable electoral boundary changes and strong support for the government from rural Malays.