Donald Trump has claimed that China’s handling of the coronavirus is proof that Beijing “will do anything they can” to make him lose his re-election bid in November.

In an interview with Reuters, the US president said he was looking at different options in terms of consequences for Beijing over the virus. “I can do a lot,” he said, without going into detail.

Trump has increasingly blamed China for the pandemic and on Wednesday again said Beijing should have let the world know about the coronavirus much sooner. He also speculated about retaliation: “There are many things I can do,” he said. “We’re looking for what happened.”

For the first time, Trump linked Beijing to his re-election chances in November. “China will do anything they can to have me lose this race,” he said, adding that he believed China wants his Democratic opponent, Joe Biden, to win the race to ease the pressure on US-China trade relations.

“They’re constantly using public relations to try to make it like they’re innocent parties,” he said of Chinese officials.

Trump said the trade deal that he concluded with Chinese president Xi Jinping aimed at reducing chronic US trade deficits with China had been “upset very badly” by the economic fallout from the virus.

The president’s attack on China appears to be in line with leaked Republican party memos, published by Politico, which advised candidates to aggressively target Beijing in their public remarks on the pandemic, as part of their re-election strategy.

Trump’s handling of the virus has come under strong scrutiny with just 43% of Americans approving of his handing of the pandemic, according to a Reuters/Ipsos poll on 27-28 April, days after the president’s discredited comments on injecting disinfectant.

Trump told Reuters he did not believe opinion polls that showed his likely Democratic presidential opponent, Joe Biden, leading the race for the White House.

“I don’t believe the polls,” Trump said. “I believe the people of this country are smart. And I don’t think that they will put a man in who’s incompetent.”

US economic figures won’t have helped Trump’s position, with news that the economy shrank at a 4.8% annual rate in first quarter of the year – a precursor to far grimmer reports expected in later months from the severe recession triggered by the pandemic.

The US is not the only country to take issue with China’s handling of the virus. Australia has called for an independent investigation into its origins, along the lines of weapons inspectors who were tasked with inspecting Iraq’s arsenal before the second Gulf war. Beijing has rejected the suggestion, saying that if that line was pursued, Chinese companies and students may not choose to do business or study in Australia. Britain’s ambassador to the US Karen Pierce said her country backed calls for an investigation but said any inquiry should come later.

In comments published on Thursday, Le Yucheng, a vice-foreign minister said China “resolutely opposes” any international investigation into the pandemic, which he described as an effort to stigmatize the country. Beijing has blamed the US for leading international criticism against China.

An English-language editorial in the nationalist state-run Global Times said the lack of US leadership was putting the entire world “under risk.” “Cooperation is the most effective solution … But if the world cannot keep a sober head on this, there will probably be a more profound crisis waiting for humanity after the pandemic is gone,” it said.

Chinese health authorities reported four new coronavirus cases on Thursday, a day after officials downgraded Beijing’s emergency response level and loosened travel restrictions, including quarantine requirements for those traveling into the capital. In a further sign Chinese officials believe the epidemic is under control within its borders, Beijing said on Wednesday that its previously delayed parliament meeting would open on May 21 and 22.

In other coronavirus developments:

• Global infections for coronavirus are approaching 3.2 million, with more than 227,000 deaths. The US leads the world on infections (1,038,451) and more than 60,000 deaths. Italy is the next worst affected by 27,682 deaths and then the UK, with 26,166.

• South Korea reported no new domestic coronavirus cases on Thursday for the first time since its 29 February peak, the Korea Centers for Disease Control and Prevention said. The country had just four new infections, all imported cases, taking the national tally to 10,765. The death toll rose by one to 247.

• Japan is expected to extend a nationwide state of emergency for another month, local media have reported, after the prime minister, Shinzo Abe, described the coronavirus outbreak as “severe”.

• The number of coronavirus cases in South Africa surged past the 5,000 marks on Thursday after it saw the largest single-day jump to date, health ministry figures showed.

• A World Health Organization official declined to comment on reports that Gilead Science’s remdesivir could help treat Covid-19, but said that further data was needed.