China supports a "comprehensive study" of all early cases of COVID-19 found worldwide and a thorough investigation into some "secretive bases and biological laboratories" all over the world, a spokesperson for the Chinese embassy in the United States said on Wednesday.

The remarks were made at a time when several US officials claimed that the investigation on virus-origin tracing in China lacked transparency and called for a strong, comprehensive and expert-led probe on the coronavirus origin.

The Chinese embassy spokesperson noted that the conspiracy theory of a "lab leak" is resurfacing, referring to the claim by some people that COVID-19 might have escaped from a laboratory in Wuhan, Hubei province.

"Lately, some people have played the old trick of political hype on the origin tracing of COVID-19 in the world. Smear campaign and blame shifting are making a comeback," the spokesperson said in a statement.

Since the outbreak of the coronavirus last year, some political forces have been fixated on political manipulation and a blame game, while ignoring their people's urgent need to fight the pandemic and the international demand for cooperation on this front, which has caused a tragic loss of many lives, the spokesperson said in the statement.

"The lesson from last year is still fresh in our memory. While the pandemic is still causing great damage in today's world and the international community is expecting greater coordination among countries, some people are turning to their old playbook," noted the spokesperson.

On the origin tracing of COVID-19, China has been calling for international cooperation on the basis of respecting facts and science, with a view to better coping with unexpected epidemics in the future, according to the statement.

It noted that to politicize origin tracing, a matter of science, will not only make it hard to find the origin of the virus, but give free rein to the "political virus" and seriously hamper international cooperation on the pandemic.

"Out of a sense of responsibility toward the health of mankind, we support a comprehensive study of all early cases of COVID-19 found worldwide and a thorough investigation into some secretive bases and biological laboratories all over the world," the spokesperson said.

Such study and investigation shall be full, transparent and evidence-based, and shall get to the bottom to make everything clear, the spokesperson added.

China reported cases of what people then called "pneumonia of unknown cause" on Dec 27, 2019, according to a white paper "Fighting COVID-19: China in Action" published in June 2020.

The World Health Organization said it received China's official report on the cluster of cases on Jan 3, 2020.

There have been studies reporting that the COVID-19 cases have been present outside of China earlier than previously known.

For example, scientists at the US Centers for Disease Control and Prevention (CDC) found evidence of infection in 106 of 7,389 blood donations collected from residents in nine states across the US as early as mid-December 2019, according to their study published online in the journal Clinical Infectious Diseases on Nov 30, 2020.

The specimens for the US study, gathered by the American Red Cross between Dec 13, 2019, and Jan 17, 2020, were sent to the CDC for retrospective testing to see if any had antibodies to SARS-CoV-2, the respiratory virus that causes COVID-19.

As a result, scientists found anti-SARS-CoV-2 antibodies in 39 samples from California, Oregon and Washington state, collected as early as Dec 13-16. Their presence indicate that isolated infections may have occurred in the western portion of the US in mid-December, according to the CDC scientists.

Antibodies also were found in 67 samples in Massachusetts, Michigan, Wisconsin or Iowa, and Connecticut or Rhode Island, collected between Dec 30 and Jan 17.

The report added to growing evidence that COVID-19 was likely present in countries such as the US, Italy and France sooner than previously thought.

In Italy, where the first COVID-19 patient was detected on Feb 20, 2020, researchers were providing evidence that the virus may have been circulating since September 2019.

The Italian researchers' findings, published by the National Cancer Institute's scientific magazine Tumori Journal on Nov 11, 2020, show that 11.6 percent of 959 healthy volunteers participating in a lung cancer-screening trial between September 2019 and March 2020 had developed coronavirus antibodies.

China Daily reported about the American and Italian studies on Dec 2, 2020.