The United Nations agency said the Saudi health ministry informed it that a 39-year-old man, who developed symptoms on February 24 and was hospitalised four days later, died on March 2.
"Preliminary investigation indicated that the patient had no contact with previously reported cases," the WHO said in a statement. "Other potential exposures are under investigation."
Novel coronavirus -- known in health jargon as nCoV -- was first detected in the middle of last year.
Including the latest victim, a total of 15 cases have now been reported.
The nine fatalities have been clustered in Saudi Arabia, Jordan and Britain. In the latter country, it affected a family, one of the members of which had visited the Middle East and Pakistan.
On Tuesday the WHO reiterated calls on its member states to remain vigilant for cases of severe acute respiratory infections and to carefully review any unusual patterns.
"The WHO is currently working with international experts and countries where cases have been reported to assess the situation and review recommendations for surveillance and monitoring," it said.
Member states should promptly assess and notify WHO of any new case of infection with nCoV, along with information about potential exposures that may have resulted in infection, it added.
"The WHO does not advise special screening at points of entry with regard to this event nor does it recommend that any travel or trade restrictions be applied," it said.
Coronaviruses cause most common colds and pneumonia, but are also to blame for unusual conditions such as severe acute respiratory syndrome, better known by its acronym SARS.
A SARS epidemic killed more than 800 people when it swept out of China in 2003, sparking a major international health scare.
The new virus however is different from SARS, especially in that it causes rapid kidney failure.