Pressure mounted on the New Zealand government Tuesday to seek parliamentary approval for any decision to send troops to help fight Islamic State (IS) insurgents in Iraq and Syria.

United States-led forces are solely using air strikes against IS positions, but Prime Minister John Key told Radio New Zealand Tuesday that US generals were saying that troops on the ground would be needed if the insurgents are to be defeated.

Key would not rule out helping with the fight, but the government would treat any request for military help cautiously.

"I'm not going to commit one way or the other to anything, other than to say we'll get some advice, we'll see how it goes, but New Zealanders can take a high degree of confidence that we'll be very considered about what we do," said Key.

Key has repeatedly said he would not send troops to Iraq and rejected suggestions that by asking for advice he was signalling a change of mind.

Phil Goff, of the main opposition Labour Party, told Radio New Zealand that Key had clearly changed his position since being re- elected on Sept. 20.

"The prime minister needs to consider that the absolute guarantee he gave, there would be no boots on the ground, before the election. Now (that) seems to have morphed into well we're getting advice, which leads many people to suspect that the request has been anticipated and the planning has already begun," said Goff.

The opposition Green Party said any commitment to military action would require the Attorney-General to provide an opinion on whether military action was legal under international law and a United Nations mandate.

Winston Peters, leader of the opposition New Zealand First party, said Key was "bowing to pressure" and steering New Zealand towards military involvement.

"Committing our defense force to a new Middle East war should not be decided on the hoof. This is a matter of serious importance, and all members of Parliament must decide," Peters said in a statement.

"Mr Key would do well to remember that when we decided not to commit troops to the Iraq War, we were applauded for being democratic and responsible in our decision making on world problems."