The US, UK and Canada have accused Russia of trying to steal coronavirus vaccine research as the pandemic surges across the world, with Brazil surpassing two million confirmed cases and the US notching a new daily record.

The virus has killed more than 588,000 people, infected more than 13.7 million and crippled the global economy since emerging late last year, and world hopes have turned to a vaccine to end the onslaught.

In the latest positive sign, British media reported Thursday that an Oxford University trial had shown its prototype vaccine generated an immune response against COVID-19.

But hours later, the UK's National Cyber Security Centre said a hacking group called APT29 had targeted British labs conducting vaccine research to "steal valuable intellectual property."

The agency said it was "almost certain (95%+) that APT29 are part of the Russian Intelligence Services" and its targeting of researchers was "highly likely (80-90%)" to "collect information on COVID-19 vaccine research."

The US, UK and Canada all accused Russia in a joint security advisory.

Moscow denied any involvement, with Kremlin spokesman Dmitry Peskov saying: "Russia has nothing to do with these attempts."

The dispute came as ever-growing tolls in Brazil and the United States, the world's two worst-hit countries, underscored the need for a vaccine.

Both passed bleak mileposts Thursday, with Brazil soaring past its two millionth infection and the US adding more than 68,000 cases in 24 hours, a new daily record.

- 'Horrible experience' -

Experts say the true case load in Brazil, home to some 209 million people, could be understated by as much as a factor of ten, and fatalities -- officially over 76,000 -- as much as twofold.

Like the US, Latin America's largest economy is led by a populist leader, Jair Bolsonaro, who has downplayed the virus and railed against restrictions.

Bolsonaro was himself diagnosed positive a week ago.

But despite the grim figures his country remains behind the United States, which has recorded by far the most deaths and infections in the pandemic, with 138,301 deaths out of a total 3,560,364 cases.

Florida is the country's new epicenter, and is shaping up as a key battleground in a partisan-tinged national fight over reopening schools in the fall.

US President Donald Trump is pushing for schools to open, pinning his re-election hopes on declaring victory over the virus and jumpstarting the economy.

Thursday also illustrated the partisan divide in the US over face masks.

Colorado governor Jared Polis issued a statewide order requiring anyone over the age of 10 to wear a mask in indoor public spaces.

Sweden tops EU for new cases

Sweden, whose softer approach to fighting the novel coronavirus drew global attention, has one of the EU's highest rates of new cases but authorities say the spread is slowing.

In the last two weeks, Sweden was only second to Luxembourg in the EU in terms of new cases per capita with new infections more than six times the European Union average.

Unlike most European nations, Sweden never imposed a lockdown and made headlines for its high death toll.

It has kept schools for under-16s open and has not shuttered cafes, bars, restaurants and most businesses. Masks have been recommended only for healthcare personnel.

Over the past 60 days, Sweden has seen a drastic increase in the number of new cases, but authorities stress that serious COVID-19 cases and associated deaths have declined.

"If you increase testing you will find more cases," deputy state epidemiologist Anders Wallensten told AFP. 

"But the more serious cases, those who become sick and need hospital care have rather decreased," Wallensten added.

In May, Sweden was testing roughly 30,000 people a week but throughout June that was scaled up and in July the figure had more than doubled.

On May 31, the country had recorded a total of 39,160 cases. On July 16, the number had almost doubled at 76,877, but deaths had only increased by just over 20 percent to 5,593.

- Row with WHO -

In late June, the rising number of cases led the World Health Organization's European branch to put Sweden on a list of 11 countries witnessing an "accelerated transmission."

But Sweden's state epidemiologist Anders Tegnell lashed out, calling it a "total misinterpretation" of data.

Sweden's Public Health Agency instead has repeatedly stressed that the large increase is mostly made up of milder cases, which would have gone unnoticed previously.

US President Donald Trump has similarly said that the surges in cases around the US are related to increased testing.

But unlike the US, the rise in cases in Sweden has not been accompanied by an increase in intensive care unit admissions.

Karin Tegmark Wisell, head of microbiology at the Public Health Agency, told AFP that the decline in serious cases is also likely a product of barrier gestures.

"People have learnt how to relate to the disease, to keep distance. We have become better at protecting the risk groups," Tegmark Wisell said.

Melbourne sees record rise in cases

Australia's second-biggest city of Melbourne reported a record rise of more than 400 new coronavirus cases on Friday despite a week-old lockdown of more than 5 million residents.

Authorities in the state of Victoria, which surrounds Melbourne, said there were 423 new infections in the metropolitan area and five more in rural parts of the state.

The total was higher than any single daily increase in COVID-19 cases for the entire country since late March. 

"We have not turned the corner here, worse than that," said Victoria's chief health officer, Brett Sutton.

Melbourne has been experiencing a surge in coronavirus infections since mid-June, after the rest of the country had successfully contained the epidemic.

The Melbourne outbreak was initially blamed on health and security breaches at hotels where returning international travellers were under quarantine.

Residents in and around greater Melbourne were ordered into a six-week stay-at-home lockdown a week ago in a bid to contain the virus, and officials said they would give those restrictions more time to counter the outbreak before considering tougher measures.

"There is a hope that the numbers stabilise over the coming days," Sutton said.

But he added: "No one is being complacent here, and we are all thinking about the additional measures that may be required if it does not turn around."

Australia's other states and territories have all closed their borders to people from Victoria in a bid to stop that outbreak from spreading.

But the contagion has already reached Sydney, where there have been growing numbers of locally transmitted COVID-19 cases in recent days after an initial cluster erupted due to an infected Melbournian visiting a popular pub.

There have been 42 virus cases linked to that pub, but officials on Friday reported several other infections with no clear link to that cluster.

US notches record 68,428 new cases

The United States on Thursday set yet another record for new coronavirus cases with 68,428 infections recorded in 24 hours, according to a tally by Johns Hopkins University.

In that period the death toll also climbed by 974 people, the Baltimore-based university's tracker showed at 8:30 pm (0030 GMT Friday).

That brought the total death toll in the country since the pandemic began to 138,201, and the total number of cases to 3,560,364.

The US remains the hardest-hit country in the world in absolute terms.

Experts believe it never emerged from its first wave of infections, and cases have been surging again in recent weeks, particularly across the south and west in states that pushed to lift lockdown restrictions early.

Florida has emerged as the epicenter of the US outbreak, reporting a record 156 COVID-19 deaths on Thursday and nearly 14,000 new infections.

The total number of virus cases in the "Sunshine State" has now surpassed 315,000, and there have been 4,782 deaths, according to Florida Department of Health figures.

Florida is now reporting more COVID-19 cases daily than any other state in the country. California and Texas are next, with about 10,000 new cases a day each.