Wellington, July 7 (IANS): New Zealand opposition on Thursday said they were vindicated over their decision to refuse to join the US-led invasion of Iraq in 2003, after the release of a report that criticised the role of the then British government in the war.

The main opposition Labour Party, which was in power under former Prime Minister Helen Clark in 2003, said it stood by its decision not to send troops to help overthrow Iraqi dictator Saddam Hussein, Xinhua news agency reported.

The official Chilcot Report on the British government's role in the war showed the Iraq invasion had sparked regional instability and left a power vacuum that was filled by the Islamic State (IS) insurgency, Labour Party leader Andrew Little said in a statement.

At the time, John Key -- the current Prime Minister -- had said New Zealand was "MIA" when the country's "traditional allies" were involved, while Clark argued the decision to go to war was not justified without a mandate from the UN Security Council.

However, Key's government has since committed forces to Iraq to train troops in the fight against the IS, with Key saying it was the price for being "in the club" of New Zealand's allies.

"The lesson for us is that going to war should never be a gung-ho decision and should certainly never be made so New Zealand can be 'in the club' with its foreign allies," said Little.

The opposition New Zealand First party said Key's government had failed to learn any lessons from the 2003 Iraq invasion.

Had Key's party been in power at the time, "they would have gone into Iraq lured by the United States, even though the invasion was based on flawed intelligence," New Zealand First defence spokesperson Ron Mark said in a statement.