PORT MORESBY – Papua New Guinea’s former and founding prime minister Sir Michael Somare has resigned from the National Alliance Party – a party he founded 20 years ago.

The Post Courier reports that Sir Michael tendered his resignation at the weekend over irrevocable differences with the party leadership over its future with the governing coalition of Prime Minister Peter O’Neill.

But the ruling People’s National Congress party remains unmoved, claiming last night that the move was only to create instability in government and did not affect its numerical strength to challenge a possible vote of no-confidence.

Somare said his reason to quit centred on his referral of Prime Minister O’Neill and other government leaders to the Ombudsman Commission for alleged breaches of the Leadership Code.

He stood by his decision, he said in his letter to party leader Patrick Pruaitch, copied to president Walter Schnaubelt and general secretary Joyce Grant, saying it was due to the Prime Minister’s alleged illegal and negligent actions.

The ABC reports that Somare resigned after being told to step down during a party meeting amid an approach by the opposition to join them and be the alternate prime minister.

Higher education minister Malakai Tabar, also a member of the ruling National Alliance (NA) party, confirmed that Somare had been approached by opposition leader Don Polye.

“Don has effectively asked the grand chief Sir Michael to be the alternate prime minister,” he said.

Tabar said the time is right for Sir Michael to resign after being forced out by current prime minister Peter O’Neill in 2012.

The minister said he supports O’Neill amid moves by the opposition to call for a motion of no-confidence in the coming weeks.

“I think the O’Neill government will survive,” he said. “The vote of no-confidence, I don’t think it’s going to help anybody.

“As a party, we are in the prime minister’s government and we are supporting him.”

Corruption cases continue to dog the O’Neill government, with some levelled against senior government ministers and the prime minister who is still subject to an arrest warrant.

Within hours of resigning from the party, Somare and fellow former prime minister Sir Mekere Morauta called for local and international authorities to investigate the government’s controversial decision to take out a loan to buy shares in an oil company.

In 2014, the PNG government took out a A$1.3 billion loan with the Australian branch of UBS bank to buy shares in the nation’s biggest company, Oil Search.

The move was controversial, with criticism over the approval and the level of debt incurred by the nation.

At a press conference on Monday, Somare and Morauta called on O’Neill to explain details of the loan following a Fairfax Media investigation which proffered a series of leaked documents alleging proper process was not followed.

“We are calling on our prime minister Peter O’Neill to explain to the nation why he has saddled Papua New Guinea with a huge financial burden with the UBS-Oil Search loan which is aggravating the government in simmering fiscal crisis,” Sir Somare said.

“Loan documents made public by the Fairfax Media group in Australia show that due process was not followed in many aspects of borrowing.

“We believe the information revealed about the transaction warrants an independent investigation by the fraud and anti-corruption directorate of the police.”

Last year, O’Neill said he stood by the decision to buy the shares and said the allegations against him were political.