The Prime Minister heads to the strict enforcer of Islam, Saudi Arabia, tomorrow.

It's a country where women have few rights, where people are beheaded and where thieves can have their hand cut off.

John Key says he'll raise human rights issues while he's there but rejects any suggestion the Saudis operate in a similar way to ISIS.

"We may not agree with the death penalty in this country - we don't - but they are doing it within their laws.

"In the case of ISIL, they don't act within the laws of their country. They're not a country, they're people that are undertaking those actions against other people quite outside of any legal process."

Women visitors to the country are expected to wear an abaya, which covers them from head to foot, leaving only their face showing.

President Obama's wife Michelle refused to cover up when she visited the country but Key says his wife Bronagh will.

"When I go to a Sikh mosque, there's plenty of pictures of me wearing appropriate headgear. That's just a reflection of respecting their culture.

"Yep, Michelle Obama went there and didn't wear an abaya, but she did completely cover herself from basically the ankles to the wrist.'

Key adds he's hoping to get as close as he can to securing a free trade deal with the Gulf Co-operation Council while he's there.

"One of the interesting things with the Gulf States, which is where we're trying to complete a free trade agreement, we actually currently sell more goods and services to the Gulf States than we do to Great Britain."