Critics of the UN report that questioned the safety of e-cigarettes have hit back, saying that the report had exaggerated their risk while underplaying their role as a safe alternative to tobacco.
The August 26 report by the UN's World Health Organisation (WHO) said governments should ban the sale of so-called electronic cigarettes to minors, warning they posed a "serious threat" to unborn babies and young people.
The WHO report, to be considered at a global meeting on tobacco control this year, also said e-cigs should be banned from indoor public spaces.
But tobacco specialists, writing in the journal Addiction on Friday, said the report was flawed.
They said it was rooted in a bigger WHO-commissioned probe, the Background Paper on E-cigarettes, which they accused of bias and error.
"We were surprised by the negativity of the commissioned review, and found it misleading and not an accurate reflection of available evidence," said Ann McNeill, a professor at the National Addiction Centre at King's College London,
"E-cigarettes are new and we certainly don't yet have all the answers as to their long-term health impact, but what we do know is that they are much safer than cigarettes, which kill over six million people a year worldwide."
E-cigarettes typically work by vaporising a liquid called propylene glycol, to which nicotine and flavouring have been added. The vapour is inhaled, like traditional cigarettes, but produces vapour instead of smoke.
The gadgets have been a huge hit with young people, who form part of a snowballing market worth about $3 billion (2.3 billion euros) annually, with more than 400 brands of flavours.
Supporters of e-cigs say the devices are a safer alternative to traditional tobacco, whose bouquet of toxic chemicals and gases cause cancer, heart disease, strokes and other ailments.
Opponents say the devices have only been around for a few years, and the long-term health impact from inhaling their industrial vapour is unclear.
The WHO report acknowledged that e-cigarettes were "likely to be less toxic" than conventional cigarettes, but more research was needed.
It also fretted that the proliferation of sweet flavours would become a "gateway to nicotine addiction" for the young.
The debate is unfolding as many governments are under pressure to impose regulations on e-cigs. At the moment, the worldwide situation is a patchwork, ranging from complete freedom of sale to bans on sales to minors or of e-cigs that contain nicotine.
The WHO failed "to acknowledge that e-cigarettes are not just less harmful than tobacco cigarettes but (also) that the concentrations of toxins are mostly a tiny fraction of what is found in cigarette smoke," the authors of Friday's commentary said.
They also took issue with concerns about risks of passive inhalation, arguing that concentrations in vapour likely to be breathed in by bystanders "are too low to present a significant health risk."
And, they said, the review suggests e-cigarettes "inhibit smoking cessation, when the opposite is true."