Iceland's Prime Minister has come under fire after leaked documents revealed that he is among other world leaders with links to secret companies in offshore tax havens. Sigmundur Davíð Gunnlaugsson walked out of an interview with Swedish television company SVT on 11 March as a journalist attempted to ask him about a company called Wintris.

The leaked documents allegedly revealed that Gunnlaugsson was the co-owner of Wintris Inc in the Caribbean island of Tortola, which was being used by him and his wife to hide millions of dollars in investments in Iceland's banks through the secret offshore company. However, Gunnlaugsson insisted that the company had been fully declared to the Icelandic tax authorities.

During the interview with SVT, Iceland's Prime Minister appears to stutter when asked about Wintris. He eventually accuses the journalists of asking "inappropriate" questions and walks out of the interview.

In the video of the interview obtained by the Guardian on 3 April, Gunnlaugsson says: "I don't know how these things work but everything is declared on the tax report from the beginning. You're asking me about things I haven't acquainted myself with. You are asking me nonsense. You trick me into an interview under false pretences. Something is being made suspicious that isn't suspicious."

The leaked documents from Panama-based law firm Mossack Fonseca were published in the German newspaper Suddeutsche Zeitung, which shared them with the International Consortium of Investigative Journalists. The information allegedly revealed that Gunnlaugsson did not declare an interest in the country when he entered parliament in 2009 and sold 50% of the secret company for $1 (70p) months later to his wife, Anna Sigurlaug Palsdottir.

The leaked documents also revealed that Wintris was used to invest millions of dollars from the sale of Palsdottir's family business. Both the prime minister and his wife were granted the power to manage the company "without any limitation", the BBC reported.

On 4 April Gunnlaugsson is expected to face a motion from opposition leaders calling for a snap general election. He will also face allegations in parliament about the fact that he has reportedly hidden a financial conflict of interest from Iceland's public since being elected as an MP seven years ago.

Iceland's former prime minister, Jóhanna Sigurðardóttir, told the Guardian: "We can't permit this. Iceland would simply look like a banana republic. No one is saying he used his position as prime minister to help this offshore company, but the fact is you shouldn't leave yourself open to a conflict of interest. And nor should you keep it secret."

According to the prime minister's office, Gunnlaugsson was never meant to have a sharehold in the company and this had been transferred to his wife in late 2009 when the error allegedly came to their attention.

Mossack Fonseca director Ramon Fonseca has denied any wrongdoing. He said the firm had suffered a hack on its database and described the leak as "an international campaign against privacy", according to Reuters.