Dr Mahathir Mohamad has pinned the temporary deregistration by the Registrar of Societies (ROS) of his party Bersatu squarely on Prime Minister Najib Abdul Razak.

"In order to win the elections, he has ordered my party Bersatu to be declared illegal.

"I am not allowed to identify myself with the illegal party," Mahathir said at an event in Petaling Jaya today.

The nonagenarian then launched into a brief tirade about Najib being called a thief abroad, but not daring to take the parties saying so, to court.

After the event, Mahathir declined to comment further on his party's deregistration.

"Tonight, tonight," he told reporters, referring to a 10PM press conference the party is scheduled to hold after a supreme council meeting.

The ROS ordered the temporary dissolution of Bersatu this afternoon for allegedly failing to submit documents requested by the registrar.

The ROS has given the party 30 days to resolve this or risk permanent deregistration.

Until then, Bersatu will not be able to use the party name or logo for any functions.

Bersatu's status had been cited by ROS director-general Surayati Ibrahim as a stumbling block to the registration of Pakatan Harapan as a formal coalition.

The Umno-splinter group, which was formed in 2016, has been facing troubles with the ROS over its annual general meeting that was held in December.

There were questions over how the national level meet was held before the branches and divisions could do so.