Jittery Americans have been watching the skies as the mysterious incursions unfolded against a backdrop of acute tensions with China -- although only the first object has so far been attributed to Beijing.

"The object has been downed by pilots from the US Air Force and National Guard," Representative Elissa Slotkin of Michigan, which lies south and west of Lake Huron, tweeted Sunday.

Another Michigan lawmaker, Representative Jack Bergman, said the US military had "decommissioned" an object over the lake.

There was no immediate confirmation from the Pentagon but Slotkin said she had received a call from the Defense Department about this new object.

"We'll know more about what this was in the coming days, but for now, be assured that all parties have been laser-focused on it from the moment it traversed our waters," she tweeted.

A senior Republican on Sunday accused Beijing of "an act of belligerence" regarding the first object, a Chinese balloon shot down February 4 off the US East Coast after American officials said it was engaged in spying.

China has insisted it was a weather balloon blown off course.

"It was done with provocation to gather intelligence data, and collect intelligence on our three major nuclear sites," Michael McCaul, chairman of the House Foreign Affairs Committee, told CBS.

US Senate Majority Leader Chuck Schumer, among senior lawmakers who received a government briefing, told ABC the second and third objects -- one shot down over Canada's Yukon territory on Saturday, and one downed over Alaska on Friday -- both appeared to be balloons, but "much smaller than" the first large one.

Reflecting the heightened state of alert, US authorities briefly closed the airspace over Lake Michigan Sunday, before the latest object was shot down further towards the Canadian border.

A similar brief closure Saturday over Montana led to the scrambling of US fighter jets, though no object was detected in that case.

Canadian Prime Minister Justin Trudeau meantime was heading Sunday to the western Yukon territory, where the third unidentified object was shot down a day earlier.

There, a US F-22 jet, acting on orders from the prime minister and US President Joe Biden, downed a "high-altitude airborne object" about 100 miles (160 kilometers) north of the border.

Canadian officials described it as small and cylindrical, roughly the size of a Volkswagen car.

Recovery teams backed by a Canadian CP-140 patrol aircraft were continuing their search Sunday for debris in the Yukon, officials said.

US teams were struggling with Arctic conditions as they searched near Deadhorse, Alaska, where the second object was shot down Friday.

Operations were also continuing off the South Carolina coast, where the past week's drama climaxed when the initial large balloon was shot down.

- 'Real concerns' -

Culminating a weekend with the military on alert, the North American Aerospace Defense Command said on Twitter that Sunday's Lake Michigan closure was "to ensure the safety of air traffic in the area during NORAD operations. The temporary flight restriction has since been lifted."

While Saturday's Montana event yielded no object at the time, a US congressman only fueled the mystery of what happened.

Montana Representative Matt Rosendale tweeted Sunday that he remained in communication with military officials "and they have just advised me that they have confidence there IS an object and it WAS NOT an anomaly."

Republicans meanwhile have harshly criticized Biden for allowing the first balloon to drift for days across the country -- potentially gathering sensitive intelligence -- before having it shot down.

Schumer on Sunday defended Biden's handling, telling ABC an analysis of recovered debris would represent "a huge coup for the United States."

But Biden has faced bipartisan calls for greater transparency.

"I have real concerns about why the administration is not being more forthcoming," Jim Himes, the top Democrat on the House Intelligence Committee, told NBC.