Source: ABC - Liam Fox

Papua New Guinea's Prime Minister has blasted his public service over the granting of controversial leases covering more than 10 per cent of the country.

In recent years more than 70 Special Agricultural and Business Leases, or SABLs, have been granted covering more than five million hectares.

Critics say the leases are a back-door way to clear-fell forests and many have been granted without the permission of traditional owners.

Greenpeace campaigner in PNG, Sam Moko, says they welcome the prime minister's comments.

"SABLs, over the years, were mainly issued through corruption and fraud," he said.

"A lot of the SABLs that are issued are issued to foreign owned companies, and it doesn't leave any benefits to the customary landowners.

"5.5 million hectares of land is a lot of land given away without proper procedures."

A Commission of Inquiry that's been investigating the leases has handed its interim report to the Prime Minister Peter O'Neill.

In a statement he says some agencies have failed to administer the law and "developers have enjoyed a free run".

Mr O'Neill says he'll table the report in the next sitting of parliament and also announce measures to improve the integrity of the public service.

The Commission's final report, which will examine each SABL, is due to be finalised in two months time.