China may have secretly conducted a nuclear test explosion despite claiming to adhere to an international pact that prohibits such explosions, according to the US State Department report.
The government's report didn't offer any proof to support its claim but said that activities at China's Lop Nur nuclear test site are concerning and that Beijing has been conducting those tests at the site all through 2019.
"China's possible preparation to operate its Lop Nur test site year-round, its use of explosive containment chambers, extensive excavation activities at Lop Nur and a lack of transparency on its nuclear testing activities ... raise concerns regarding its adherence to the zero yield standard," according to the government document.
Zero yields refers to a nuclear test in which there is no explosive chain reaction of the type ignited by the detonation of a nuclear warhead.
The findings, first published by WSJ, could worsen the already strained relationship between the two countries.
US also blamed China for COVID-19
Earlier, the US had also alleged that the global COVID-19 pandemic resulted because of Beijing's mishandling of the outbreak in Wuhan where it first emerged in December 2019.
Nuclear tests ban under CTBT
Nuclear test explosions are banned under the Comprehensive Test Ban Treaty (CTBT)-of which both the US and China are signatories but none has ratified it. However, China has promised to adhere to its norms whereas the US has been observing a unilateral moratorium on nuclear tests since 1992.
Were the treaty ratified, member nations would be obliged to allow inspection of sites causing concern.
As per the US document claim, Bejing's lack of transparency included blocking data transmission from five sensors linked to an international monitoring centre operated by CTBT.
On questioning, the spokesperson for the CTBT, however, denied interruption of transmission from China's five sensor stations since August 2019.
China refutes claim
The Chinese government denied the accusations and said the US is making false allegations.
Speaking at a press briefing, Chinese foreign ministry spokesman, Zhao Lijian said that "China has always adopted a responsible attitude, earnestly fulfilling the international obligations and promises it has assumed."
Refuting the allegations he said, "The U.S. criticism of China is entirely groundless, without foundation, and not worth refuting."
Attempt to force China to sign New START treaty
Many believe that the allegations against China could be an attempt by the US to sign an arms control treaty, 2010 New START. Currently, the US and Russia are signatories of the treaty which is going to expire in February next year. The US wants both China and Russia to join it.
New START restricted the United States and Russia to deploying no more than 1,550 nuclear warheads, the lowest level in decades, and limited the land- and submarine-based missiles and bombers that deliver them.
Addressing the report, a US government official with knowledge about the matter said, "The pace and manner by which the Chinese government is modernizing its stockpile is worrying, destabilizing, and illustrates why China should be brought into the global arms control framework,". The senior U.S. official said this to Reuters on condition of anonymity.
China claims nuclear force poses no threat
China, estimated to have about 300 nuclear weapons, has repeatedly rejected Trump's proposal, arguing its nuclear force is defensive and poses no threat.
Russia, France and Britain - three of the world's five internationally recognized nuclear powers - signed and ratified the Comprehensive Test Ban Treaty, which still requires ratification by 44 countries to become international law.
(With inputs from Reuters)