Leaders of China and Russia have pledged to counter the “politicisation” of the coronavirus pandemic as Beijing faces mounting international backlash for its early handling of the outbreak. “Politicitising and labelling the pandemic will not benefit international cooperation, and China and Russia should cooperate closely and safeguard global health care security together,” Chinese President Xi Jinping told his Russian counterpart Vladimir Putin , according to a statement by the Chinese foreign ministry. Putin responded by saying that any attempt to discredit China was unacceptable. He said Moscow would work closely with Beijing and under the United Nations system in the pandemic fight. “Russia and China have always been united and cooperated and supported each other, which demonstrates the strategic and high-level Russia-China relations,” the Russian president said. “Some people tried to tarnish China on the issue of the virus origin and that is not acceptable.” This was the second phone conversation between Xi and Putin since the coronavirus outbreak first started in the central Chinese city of Wuhan in late December. The show of unity came at a time when Beijing had come under growing international criticism and had been accused of lacking transparency and responding too slowly to the outbreak. The outbreak has since developed into a pandemic and has killed more than 144,000 people across the world, including more than 22,000 in Italy and nearly 20,000 in Spain. In the United States, where more than 670,000 people have been infected and more than 34,000 people have died, intelligence and national security officials are looking into the possibility that the novel coronavirus escaped from a Chinese virology lab instead of a wet market as China had claimed. “More and more, we’re hearing the story,” US President Donald Trump said at a briefing on Thursday without elaborating on what that story was. “We are doing a very thorough examination of this horrible situation.” Britain is also reportedly investigating the origin of the pandemic, including the possibility that it was linked to the Chinese lab in Wuhan where scientists had conducted bat disease research, according to Sky News. British Foreign Secretary Dominic Raab, who is deputising for Prime Minister Boris Johnson as Johnson recovers from Covid-19, a disease caused by the coronavirus, said on Thursday that a “deep dive” was needed to review the virus spread. “But there is no doubt we can't have business as usual [with China] after this crisis, and we will have to ask the hard questions about how it came about and how it couldn't have been stopped earlier,” Raab said. When asked about the claim on Thursday, Chinese foreign ministry spokesman Zhao Lijian said the accusation “lacks scientific evidence”. China has emerged from more than two months of lockdown to an economic standstill . The risk of a secondary outbreak caused by imported infections is high. In an effort to contain imported infections last week Beijing closed its checkpoints on land borders with Russia after more than 500 new cases were brought in by Chinese nationals travelling from Russia. Russia confirmed 658 new coronavirus infections , bringing the official number of cases to more than 27,000. Xi told Putin that China would continue to offer “firm support” to Russia.