WASHINGTON (AP) - The Pentagon shot down an unknown object flying in U.S. airspace off the coast of Alaska on Friday on orders from President Joe Biden, White House officials said.

The object was flying at about 40,000 feet and posted a “reasonable threat” to the safety of civilian flights, said John Kirby, White House National Security Council spokesman. He described the object as roughly the size of a small car.

It was the second time in a week U.S. officials had downed some type of flying object over the U.S. On Saturday fighter jets shot down a suspected Chinese spy balloon off the coast of South Carolina.

White House officials drew major differences between the two episodes. Kirby said it wasn't yet known who owned the object, and he did not say that it was a balloon. Officials also couldn't say if there was any surveillance equipment on it. He also didn't know yet where it came from or what its purpose was.

Kirby said fight pilots visually examining the object ascertained that it was not manned.

The object fell into frigid waters and officials expected they could recover debris faster than from last week's massive balloon.

The development came almost a week after the U.S. shot down a suspected Chinese spy balloon off the Carolina coast after it traversed sensitive military sites across North America. China insisted the flyover was an accident involving a civilian craft and threatened repercussions.

Biden issued the order but had wanted the balloon downed even earlier. He was advised that the best time for the operation would be when it was over water. Military officials determined that bringing it down over land from an altitude of 60,000 feet would pose an undue risk to people on the ground.

China responded that it reserved the right to “take further actions” and criticized the U.S. for “an obvious overreaction and a serious violation of international practice.”