British Prime Minister Boris Johnson announced yesterday that he is self-isolating after testing positive for COVID-19. Meanwhile, Chinese President Xi Jinping, in a call with US President Donald Trump yesterday, said China and the United States should ‘unite to fight’ the deadly coronavirus pandemic. The two countries have clashed in recent weeks over the virus, and Chinese state media said Xi told Trump he hoped the “US will take substantive actions to improve Sino-US relations.”

“I am now self-isolating, but I will continue to lead the government’s response via video-conference as we fight this virus,” he wrote. “Be in no doubt that I can continue thanks to the wizardry of modern technology to communicate with all my top team to lead the national fightback against coronavirus,” he added in the video message.

A Downing Street spokesperson said in a statement that Johnson, whose partner Carrie Symonds is pregnant, experienced mild symptoms on Thursday and was tested for COVID-19 on the personal advice of England’s chief medical officer. The test was carried out in No 10 by NHS staff, the spokesperson added. In his video message, Johnson thanked workers in Britain’s state-run National Health Service (NHS) for their efforts in battling the spread of the virus. A total of 11,658 coronavirus cases have so far been confirmed in Britain, and 578 deaths. Earlier this week Prince Charles, the eldest son and heir to Queen Elizabeth II, also tested positive for the virus. The government confirmed this week that if Johnson was incapacitated, Foreign Secretary Dominic Raab would temporarily assume the role of prime minister. Meanwhile, UK Health Secretary Matt Hancock said he had tested positive for COVID-19.

“Following medical advice, I was advised to test for #Coronavirus. I’ve tested positive. Thankfully my symptoms are mild and I’m working from home & self-isolating,” Hancock announced on Twitter. In his response to the Chinese president’s call, Trump sounded a positive tone, tweeting that he had a “very good conversation” with Xi, and that both leaders discussed the pandemic “in great detail”.

“China has been through much & has developed a strong understanding of the virus. We are working closely together. Much respect,” he wrote. Trump and his Secretary of State Mike Pompeo angered Beijing this month by repeatedly referring to “the Chinese virus” when discussing the COVID-19 outbreak first detected in the Chinese city of Wuhan.

Trump has since dropped the term amid accusations of racism, in another small sign of easing tensions between the two world powers. Earlier this month a foreign ministry spokesman in Beijing also suggested in a tweet that the US military brought the virus to Wuhan. This prompted Trump to accuse China of spreading misinformation, and the US president repeatedly attacked China’s lack of transparency and the slowness of its initial response to the outbreak.

Xi said Sino-US relations were at a “critical juncture”, CCTV reported, adding that cooperation was mutually beneficial and “the only right choice.” Friday’s call also took place as the US overtook China as the country with the most confirmed coronavirus cases—the pathogen has now infected more than 82,400 people in the world’s largest economy. During the call, Xi said China had shared information about the epidemic with the World Health Organization and other countries including the US in a “timely” manner throughout.

“Infectious diseases are the common enemy of mankind, and do not recognise borders or races,” said Xi. Some provinces, cities and companies in China have provided medical supplies and support to the US as well, Xi added. At an emergency videoconference chaired by Saudi Arabia Thursday—which both Xi and Trump joined—G20 nations pledged a “united front” in the fight against the coronavirus. The group said they would inject $5 trillion into the global economy to counter the pandemic amid forecasts of a deep recession.