"Her murder does not end her vision and must not be allowed to empower her assassins. Those responsible – within and outside of government -- must be held accountable," Asif Ali Zardari wrote in a commentary in the Washington Post.

"I call on the United Nations to commence a thorough investigation of the circumstances, facts and cover-up of my wife's murder, modelled on the investigation into the assassination of former Lebanese Prime Minister Rafiq al-Hariri," he said.

Zardari also called on the ‘friends of democracy in the West’, particularly the US and Britain, to support such an investigation.

"An investigation conducted by the government of Pakistan will have no credibility, in my country or anywhere else," he wrote.

"One does not put the fox in charge of the henhouse."