American officials said Wednesday that the spy balloon shot down on Saturday was part of a fleet of balloons China is using in a massive surveillance program—but China is continuing to insist it was a wayward weather balloon. At a briefing Thursday, Chinese Foreign Ministry spokesperson Mao Ning said the balloon was a civilian research airship that been been blown off course and the US "overreacted," the AP reports. The American accusations "may be part of the US side’s information warfare against China," Mao said, calling the US "irresponsible." Brig. Gen. Pat Ryder, the Pentagon press secretary, said the US is "100% clear" that the balloon was not being used for "civilian purposes." An exec at Kaymont, an American firm that sells weather balloons globally, tells Reuters that the Chinese balloon had a size, flight time, and payload far in excess of a typical weather balloon. Jesse Geffen says even the larger balloons that carry photo and video equipment are less than a third of the size of the Chinese balloon. The US says it has shared information on the surveillance program with dozens of countries, including allies in Asia and elsewhere who were also targeted. Despite deteriorating US-China relations, a spokeswoman for China's Commerce Ministry said Thursday that Beijing would welcome a visit by Treasury Secretary Janet Yellen, the South China Morning Post reports. "It is very important for both sides to maintain normal communication," Shu Jueting said. “China welcomes a trip by Secretary Yellen.”More From NewserSpain Ordered New Trains, Forgot One Important ThingAfter Putin Doubles Down, Biden Does, TooAncient Empire's Crown Jewels Found 'in the Back of a Car'This article originally appeared on Newser: China Doubles Down on Weather Balloon Claim