The B117 coronavirus variant, first reported in the UK, has been found in at least 60 countries, 10 more than seven days ago, the World Health Organisation said on Wednesday.
It also said the South African variant was reported in 23 countries and territories.
Both the UK and South African variants are believed to be up to 70 per cent more transmissible than early strains.
The number of deaths reached a high of 93,000 in the previous week, with 4.7 million new cases reported, the WHO said.
Concerns over the increased infectivity of new strains caused governments around the world to toughen constraints as authorities try to slow infections until vaccines become widely available.
Covid-19 has caused more than two million deaths globally since it was first detected in the Chinese city of Wuhan more than a year ago, while the number of reported cases is edging towards 100 million, according to Johns Hopkins University data.
The US is by far the worst-hit nation, having recorded more than 400,000 deaths. President-elect Joe Biden focused on healing at a memorial for victims of the pandemic on the eve of his inauguration.
"It's hard sometimes to remember but that's how we heal. It's important to do that as a nation," Mr Biden said on Tuesday at the National Mall reflecting pool in Washington, where lights were turned on as a memorial to those who died.
"Let us shine the lights in the darkness along the sacred pool of reflection and remember all who we lost."
Almost a year after the US registered its first fatality, the pace of the pandemic has picked up, with 100,000 deaths reported in the past month alone.
Mr Biden made tackling the pandemic his top priority as he prepared to take office in Washington on Wednesday.
He is already being forced to take action, with his aides rejecting a move by outgoing President Donald Trump to lift an entry ban for travellers from Europe and Brazil.
