Global cases of Covid-19 approached 1.5 million, as both the US and the UK recorded their deadliest day yet in the pandemic, and a fresh World Health Organization row erupted.

The Chinese Communist Party said on Tuesday that it was investigating an outspoken property tycoon who accused China’s top leader, Xi Jinping, of having mishandled the coronavirus outbreak.

British Prime Minister Boris Johnson was in intensive care Tuesday fighting the coronavirus, while authorities in New York and elsewhere in Europe hoped that an apparent plateau of deaths and new hospitalizations signaled that key epicenters in the global pandemic had turned a corner.

Ever since President Richard Nixon signed the Shanghai Communique in 1972 that began the process of establishing relations between the United States and China, which was followed seven years later with the passage of the Joint Communiqué on the Establishment of Diplomatic Relations officially normalizing relations between the two adversaries.

A senior British government minister said Boris Johnson was able to continue running the country despite being admitted to a London hospital for persistent coronavirus symptoms.

The C.I.A. has been warning the White House since at least early February that China has vastly understated its coronavirus infections and that its count could not be relied upon as the United States compiles predictive models to fight the virus, according to current and former intelligence officials.