The United States so far has no evidence that three unidentified aerial objects shot down this month were connected to China or any foreign spying program, the White House said Tuesday.

US authorities "thus far haven't seen any indication or anything that points specifically to the idea that these three objects were part of the PRC's spy balloon program or that they were definitely involved in external intelligence collection efforts," National Security Council spokesman John Kirby told reporters, using the Chinese state's official acronym.

Kirby said the three objects -- two shot down over the United States and one over Canada -- "could be balloons that were simply tied to commercial or research entities and therefore benign."

That "could emerge as a leading explanation here," he said.

However, Kirby stressed that China is running a "well funded, deliberate program" to use high-altitude, hard-to-detect balloons for spying on the United States and other countries.

Such a balloon, according to American officials, was shot down on February 4 over the US East Coast -- an incident that triggered a heightened alert, leading to the precautionary shooting down of the subsequent three unidentified objects.

Beijing denies it uses spy balloons and says the huge craft shot down off the coast was for weather research.

According to the Pentagon and the White House, getting to the bottom of the three mystery objects is made harder by the difficult conditions for teams sent to find the debris.

Citing "pretty tough" weather and geographical conditions in all three cases, Kirby said "we're recognizing that it could be some time before we locate and recover the debris."

"We haven't found them yet," he said.