Orders have been issued for the arrest of Papua New Guinea’s opposition leader.

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.

A police spokesman told AAP the order for Mr Namah’s arrest was issued on Saturday morning.

Further comment is being sought from police.

Mr Namah is expected to give a press conference on Saturday night.