A group of over 50 leading scientists has told the World Health Organization classifying e-cigarettes as tobacco products could seriously hamper the international campaign against tobacco use.

The UN agency, which is currently studying the matter and hasn't yet taken a position, previously indicated it would likely favor restrictions on all nicotine-containing products, which includes e-cigarettes.

But, days before the so-called World No Tobacco Day, the scientists from Europe, North America, Asia and Australia have sent an open letter to WHO Director General Margaret Chan, asserting that low-risk products like e-cigarettes are "part of the solution" in the fight against smoking, according to a report by Reuters.

"These products could be among the most significant health innovations of the 21st century -- perhaps saving hundreds of millions of lives. The urge to control and suppress them as tobacco products should be resisted," the letter said.

Reports generated from a meeting last November suggested the WHO views e-cigarettes as a "threat" and wants them classified the same way as regular tobacco products under the Framework Convention on Tobacco Control, said the Reuters story.

That potentially negative classification has alarmed medical experts, and also e-cigarette industry representatives, across the globe.

Aside from the United States, the lone non-signator, 178 countries are parties to the international convention and obliged to follow its restrictions.

Therefore, an effort to classify e-cigarettes with regular cigarettes would force countries to follow similar efforts to restrict demand for tobacco through methods like raising taxes, banning advertising, introducing health warnings and curbing use in public places, the Reuters report continued

Sales of electronic cigarettes, which use battery-powered cartridges to produce a nicotine-laced inhalable vapor, have jumped over the last two years to an estimated $3 billion worldwide.

E-cigarettes have caused controversy since their introduction into the market; since they are so new there's a lack of long-term scientific evidence to support their safety, said the Reuters piece.

As a result, many fear the devices could actually prove a "gateway" to nicotine addiction and tobacco smoking, although the scientists behind the written appeal to Chan said they were "unaware of any credible evidence that supports this conjecture."

In Europe alone, approximately 7 million people use e-cigarettes, invented in China in the early 2000s.

Addiction specialist Gerry Stimson, an emeritus professor at University College London who co-signed the letter to Chan, explained to reporters that e-cigarettes have been shown to release "very, very fractional levels" of toxins compared to regular cigarettes.

"People smoke for the nicotine and die of the tar ... if you separate the nicotine from the burning of vegetable matter," he said. "People can still use nicotine but they're not going to die from smoking."

A recent study of nearly 6,000 people who quit smoking in England between 2009 and 2014 showed they were 60 times more likely to succeed using e-cigarettes, as compared to nicotine patches or gum, or, harder yet, going "cold turkey" and completely quitting, abruptly.

In response to the scientists' letter, Penny Woods, chief executive of the British Lung Foundation, told Reuters: "The overall impact of e-cigarette use on public health is currently unclear. While they could prove to be an important tool to help people stop smoking, the unregulated status of e-cigarettes is problematic."