At least 1,338 of the iconic animals were killed for their horns in Africa last year.
This is the greatest loss in a single year since an intense wave of poaching began recently.
Since 2008, as many as 5,940 rhinos have been killed although scientists fear that could be an underestimate.
The findings were compiled by researchers from the International Union for the Conservation of Nature (IUCN).
The losses come despite a drive to fight poaching gangs by strengthening patrols, harnessing satellite technology and boosting intelligence-gathering.
The IUCN blames continuing demand from South East Asia - where rhino horn is wrongly believed to have medicinal properties - fed by increasingly sophisticated international crime networks.
Officials say that amid the killings there are some helpful developments.
Overall, the rate of increase in poaching has fallen slightly and in South Africa, home to the greatest number of rhinos, the numbers killed in a single year fell slightly for the first time since 2008.
Dr Richard Emslie, of the IUCN's African Rhino Specialist Group, told the BBC:
"Any increase in poaching is alarming but there are some positives. When poaching started to escalate in 2008, we saw year after year of exponentially increasingly poaching.
"But over the last couple of years we've seen a decline in the rate of increase."
Dr Emslie described this as "an encouraging trend" and he highlighted how South Africa has managed to reduce the number of rhinos slaughtered from 1,215 in 2014 to 1,175 last year.
But success in one area can lead to further poaching elsewhere and while South Africa can point to a slightly improved picture, other countries have seen sharp increases in losses.
According to the new data, the number of rhinos killed in Namibia has quadrupled in just the last two years while losses in Zimbabwe doubled over the same period.
Dr Emslie described the fight against poaching as like squeezing a balloon.
"If you clamp down on poaching on the one side of the Kruger National Park beside the Mozambique border, then suddenly the balloon pops out a bit the other side and you can get more poaching.
"There's a trend of poaching  from different park to different park and also from one country to another so no individual country is safe and all need to be on their guard given the huge threat."
Commenting on the latest figures, Craig Bruce, a rhino specialist at the Zoological Society of London, said: "I think it's a dire situation and despite reports of a decrease in the Kruger National Park, I don't think it's a cause for celebration.
"If we continue with the current rate of losses, then I would estimate that within five to 10 years, all we will have is rhinos in very strictly controlled captivity scenarios and we will basically have lost the species in the wild."
After a previous collapse in rhino numbers during the 1960s, a concerted effort which was backed by determined governments and generous funding saw populations restored.
But this crisis is seen as more serious and therefore harder to tackle because of the sheer aggression and growing sophistication of the poaching gangs, fuelled by the high price for rhino horn on the black market.
Mr Bruce told me that every new technological advance designed to help the conservation effort - including drones, radios and intelligence-gathering - is matched by the poachers.
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"What's frightening is that the same technology that we are able to use, they are also able to use. Shockingly, as much as we're using them to combat the poachers, they're using them to facilitate their poaching.
"They understand intelligence as well as we do. They understand how to threaten people to get information, how to threaten people to keep them quiet so the whole criminal element has just advanced in a way that's unprecedented."
The latest data will reignite long-running debates over the best way to stem the losses.
Ideas range from cutting off the rhinos' horns in order to deny poachers and to flood the market with cheap horn to fitting monitoring devices or even cameras to the animals to help provide warning of attacks.
With the global total of rhinos now only in the region of 25,000, there will be renewed attention in the approach to a major international meeting of the CITES convention, set up to combat the illegal trade in endangered species, in Johannesburg in September.
And the South African government has just announced the logo for the event: an image of a rhino.
The mass slaughter of rhinos has increased for the sixth year in a row, according to grim new figures from international researchers.