In a report, the Geneva-based agency found that the boom in e-cigarettes presents a public health dilemma.
Regulation "is a necessary precondition for establishing a scientific basis on which to judge the effects of their use," it said.
Little is known about the health effects of e-cigarettes, which have been sold in the U.S. since 2007 and contain less toxic substances than traditional cigarettes do. The biggest markets are Europe and North America, where U.S. regulators in April proposed treating e-cigarettes as tobacco products with rules such as a ban on sales to those under 18 and warning labels.
Sales are banned in 13 of the 59 countries that regulate the devices, the WHO reported, but most of those 13 countries say they are still available because of illicit trade and cross-border Internet sales.
The WHO report, requested in 2012 by the 179-nation WHO treaty for controlling tobacco, is to be discussed at a conference in Moscow in October. If the recommendations are adopted, the next step would be for nations to strengthen their laws and policies to meet the treaty obligations.
Transnational tobacco companies are aggressively competing with independent companies for market share and the rapid growth of e-cigarettes' use globally means appropriate regulation is needed, the WHO said.
"E-cigarettes are a story of both risks and promises. In a sense they are a double-edged sword," Dr. Douglas Bettcher, director of WHO's Department for Prevention of Non-communicable Diseases, told reporters. "The tobacco industry is taking greater share — as public health partners pretending to be part of the solution to the health disaster they have created."
Tommaso Di Giovanni, head of reduced-risk product communications at Philip Morris, criticized the WHO for calling for a "de facto exclusion of tobacco companies in the democratic process."
"This view ignores the fact that product innovation to develop and assess truly reduced risk alternatives to combustible cigarettes can play an important role for public health," he said in an email to the Associated Press. "Companies like ours are not only driving this innovation, but have the necessary knowledge and resources to contribute to achieving that goal."
A day earlier, the American Heart Association urged more regulation particularly to keep them out of the hands of young people and said it supported the use of the battery-powered devices that vaporize nicotine only as a last resort to help smokers quit.