Asymptomatic cases are those who carry the virus but display no symptoms of illness such as fever. There were no immediate further details about the 12 cruise ship cases from the WHO.
WHO epidemiologist Maria van Kerkhove said on Thursday the organization did not believe transmission of the disease by asymptomatic people was a major factor fueling its spread.
"We know that that is possible but we do not believe that is a major driver of transmission," she told a Geneva news briefing.
."..If we look at the actual epidemics and how these epidemics are unfolding, if they were a major driver of transmission it would have caused much larger numbers of cases."
Through tracing people exposed to the virus in some countries, people who have not yet developed symptoms are being identified, she said. "So these are people who are pre-symptomatic, so it is a few days before they develop symptoms," she added.
The cruise ship was heading to the southern city of Luxor from Aswan, the WHO and health ministry said in a joint statement. It is unclear how many people were on board at the time.
The 12 cases were diagnosed after a Taiwanese American woman who had been on the cruise tested positive for the coronavirus upon her return home, the statement said.
The woman is believed to be the individual who spread the virus to the others, according to the statement.
The 12 new cases will be transferred to the isolation facility and all others who had been in contact with them will be placed under a 14-day quarantine, the ministry said.Egypt had until now diagnosed only three people with the virus, one of whom it said had fully recovered after receiving treatment.