Pakistan's Prime Minister Nawaz Sharif addressed the nation by television on Tuesday to defend his family's business practices, denying any wrongdoing and calling corruption claims "old accusations repeated over and over again".

Sharif set up a commission on Tuesday to investigate allegations, based on leaked documents from Panama, that offshore companies headed by members of his family were avoiding paying taxes or disguising assets and their origins.

On Monday, leaked documents from the Panama-based Mossack Fonseca law firm showed that Sharif's daughter Mariam and sons Hussain and Hassan owned at least three offshore holding companies registered in the British Virgin Islands. Mossack Fonseca denied any wrongdoing.

The International Consortium of Investigative Journalists said these companies were involved in the purchase and mortgage of at least $13.8mn in UK properties.

One of the holding companies also purchased another, Liberia-based, holding company for $11.2mn in August 2007, according to the documents.

The documents do not show the source of the assets held by the holding companies. They are part of a tranche of 11.5mn documents leaked by the ICIJ, dubbed the 'Panama Papers'.

Political opponents in Pakistan, notably Imran Khan, have accused Sharif's family of having gained the funds illegally through corruption during his two previous stints as prime minister in the 1990s.

Sharif and his family have denied any wrongdoing, saying the assets were gained legally, mainly through the family's network of businesses and industries in Pakistan and Saudi Arabia.

"I say that those who are repeating tired accusations should go before this commission and prove their accusations," Sharif said in his televised speech.