ORDERS have been issued for the arrest of Papua New Guinea's opposition leader amid allegations he threatened the nation's police commissioner.

The country's top cop, Tom Kulunga, on Saturday ordered the arrest of Belden Namah on allegations the former deputy prime minister threatened him in a letter.

In the letter Mr Namah allegedly demanded Mr Kulunga reinstate four policemen who were suspended after a warrant was issued for the arrest of Prime Minister Peter O'Neill.

"Failure to accede to my request will result in me taking unprecedented measure to have you arrested and charged under Section 128 of the Criminal Code," Mr Namah is alleged to have said in a letter to Mr Kulunga on Friday.

Mr Kulunga said the statement amounted to a threat.

"I will not allow the actions of an impatient, irrational and erratic man to threaten peace and stability within the country. He will be arrested forthwith for threatening," Mr Kulunga said in a statement.

"We are fed up with the tantrums of the Opposition Leader who is acting like an impatient, insensitive and thoughtless child.

"He does not respect the rule of law nor does he respect the systems and processes in place."

AAP understands Mr Namah is at his residence near Parliament House in Port Moresby.

Mr Kulunga said the matter of the suspended officers was due to be heard by a court on Monday.

"And yet he has seen fit to write to me and threaten to arrest me over this matter," Mr Kulunga said.

"The Opposition Leader thinks he can take on the roles and responsibilities of everyone.

"Here he is a complainant, an investigator, a prosecutor and now he wants to be the judge also."

Mr Namah was PNG's deputy prime minister until he split with Mr O'Neill just before the 2012 election.

As deputy prime minister, Mr Namah once stormed the Supreme Court and demanded the arrest of the nation's Chief Justice.

More recently, the former military officer demanded the arrest of Mr O'Neill on allegations he ordered illegal payments of state money to controversial law firm Paul Paraka lawyers.

Mr O'Neill repeatedly denied the allegations and has called Mr Namah a nuisance.

Last week he ordered police to investigate Mr Namah and the four police officers, after a court issued a warrant for the arrest of Mr O'Neill, his treasurer Don Polye and Finance Minister James Marape.

The country's anti-corruption watchdog, Taskforce Sweep, says its investigations have not turned up enough evidence to charge the prime minister.

Mr O'Neill controls a coalition government of more than 90 MPs out of 111.

Mr Namah leads an opposition of about five MPs.

Comment has been sought from Mr Namah.