The unidentified flying object shot down in Canadian airspace on Saturday appeared to be a "small, metallic balloon with a tethered payload below it," according to a Pentagon memo sent to lawmakers on Monday and obtained by CNN.

The memo offers the first official details of one of the three objects shot down in recent days that was previously described as a "cylindrical object."

The object crossed near "US sensitive sites" before it was shot down, the memo said.

Defense officials also wrote in the memo to lawmakers that the object shot down over Lake Huron, in Michigan on Sunday, "subsequently slowly descended" into the water after impact.

The new details in the memo come as lawmakers on Capitol Hill are pressing to gain a better understanding of why the Biden administration shot down three unidentified objects in three days following the take down of the Chinese spy balloon that traversed the US the previous weekend.

Lawmakers and congressional aides told CNN that the consecutive shoot-downs felt on the surface like an overcorrection to the Chinese spy balloon incident, though they cautioned that it was still too early to say definitively.

"My speculative guess as why we're seeing these things happen in quick succession is now we're really attuned to looking for them, right?" Rep. Jim Himes of Connecticut, the top Democrat on the House Intelligence Committee, said on NBC's "Meet the Press" Sunday.

"The truth is that most of our sensors and most of what we were looking for didn't look like balloons. Now, of course, we're looking for them. So, I think we're probably finding more stuff," Himes added.

The Senate is holding a classified briefing for all senators on the shot down objects on Tuesday, according to a spokesman for Majority Leader Chuck Schumer.

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• Can aliens be ruled out? Top US official asked crucial question about strange objects floating above North America
• What we know and don't know about the Chinese balloon

The White House on Monday denied that President Joe Biden's recent swift actions to take down high-altitude objects identified hovering over American airspace were the result of political pressure, following earlier critiques that he waited too long to make the call to shoot down a suspected Chinese spy balloon.

"These were decisions based purely and simply on what was in the best interest of the American people," National Security Council coordinator for strategic communications John Kirby said Monday.

A defense official said that the radar used by North American Aerospace Defense Command (NORAD) was adjusted after the initial high-altitude balloon sighting. "We continue to refine detection settings, and that won't stop just because we have identified these smaller objects," the official said.

A US official told CNN this past weekend there has been caution inside the administration on the pilot descriptions of the unidentified objects due to the circumstances in which the objects were viewed.

"These objects did not closely resemble and were much smaller than the PRC balloon and we will not definitively characterize them until we can recover the debris, which we are working on," a National Security Council spokesperson said.

The memo says that the object shot down over Alaska on Friday was the "size of a small car" and not similar to the Chinese balloon shot off the coast of South Carolina.

"We have no further details about the object at this time, including the full scope of its capabilities, its purpose, or its origin," the Pentagon memo says.

The memo said that "recovery/exploitation" efforts were underway to retrieve the object shot down in Canada's Yukon territory, noting that both US and Canadian officials were attempting to identify debris.

Canadian officials are leading that investigation, though the FBI was embedded with them, according to the memo.

"It should not be assumed that the events of the past few days are connected," the Pentagon noted in the memo.

US Coast Guard ships were deployed to search the site in Lake Huron where the third object was shot down, and the Pentagon memo said no additional information was available about the description of that object.

"The priority is now recovery and exploitation of the object," the memo said.a