Armenian President Armen Sarkissian has tested positive for Covid-19 and is in isolation in London where he had been spending the new year with his family, his office said on Tuesday.
Mr Sarkissian, 67, "had symptoms of the novel coronavirus", the presidency said.
Sarkisian had been in London to "spend the New Year with his family and grandchildren", and to have an operation on his leg, it said.
"The president is in self-isolation and will continue temporarily to carry out his role at a distance," it said.
The role of president in Armenia is largely ceremonial and executive power rests mainly with Prime Minister Nikol Pashinyan, who caught the virus in June along with his family.
The small Caucasus country, home to about three million people, has badly struggled to contain the effects of the pandemic.
It has had a total of 160,000 cases and 2,878 deaths so far, the latest official figures showed on Tuesday.
Armenian authorities have been criticised for their handling of the outbreak.
Experts say the decision to close the borders came too late and that citizens were confused by contradictory messages from officials.
The situation was aggravated by six weeks of fighting between Azerbaijan and separatists backed by Armenia for control of the disputed Nagorno-Karabakh region.
In early November, a peace deal mediated by Russia ended the conflict, which left more than 6,000 people dead.