President Joe Biden said Thursday that the U.S. is developing “sharper rules” to track, monitor and potentially shoot down unknown aerial objects, following three weeks of high-stakes drama sparked by the discovery of a suspected Chinese spy balloon transiting much of the country.

The president has directed national security adviser Jake Sullivan to lead an “interagency team” to review U.S. procedures after the U.S. shot down the Chinese balloon, as well as three other objects that Biden said the U.S. now believes are most likely “benign” objects launched by private companies or research institutions.

While not expressing regret for downing the three still-unidentified objects, Biden said he hoped the new rules would help “distinguish between those that are likely to pose safety and security risks that necessitate action and those that do not.”

“Make no mistake, if any object presents a threat to the safety and security of the American people I will take it down,” he added, repeating the legal justification cited for the downings — that the objects, flying between 20,000 and 40,000 feet posed a remote risk to civilian planes.

The downing of the Chinese surveillance craft was the first known peacetime shootdown of an unauthorized object in U.S. airspace — a feat repeated three times a week later.

Biden sharply criticized China’s surveillance program, saying the shootdown sent a “clear message, the violation of our sovereignty is unacceptable,” but said he looks to maintain open lines of communication with Beijing. Secretary of State Anthony Blinken postponed his first planned trip to China as the balloon was flying over the U.S., and a new meeting with his Chinese counterpart has yet to be scheduled.

“I expect to be speaking with President Xi and I hope we can get to the bottom of this,” Biden said, adding, “But I make no apologies for taking down that balloon.”

Biden said the rules would remain classified so as not to “give a roadmap to our enemies to try to evade our defenses.”

Rep. Jim Himes of Connecticut, the ranking Democrat on the House Intelligence Committee, said he expected the U.S. would keep its radar systems set going forward to detect slow-moving balloons as well as fast-moving aircraft and other possible intruders. But he said he had impressed on White House officials late Tuesday that security forces would have to fine-tune their response for when they spot balloons of unknown provenance.

“The White House scrambling fighters and tankers” and special forces, he said, “is not going to be a scalable solution to every bit of airborne junk.”

The Chinese balloon has escalated tensions between the U.S. and China. Blinken travels Thursday to the Munich Security Conference and there is speculation he might use the opportunity to meet top Chinese foreign policy official Wang Yi, who will also be attending the conference.

Biden had remained largely silent on the objects downed Friday off the coast of Alaska, Saturday over Canada and Sunday over Lake Huron. On Monday, the White House announced earnestly there was no indication of “aliens or extraterrestrial activity.” By Wednesday, U.S. officials said they were still working to locate the wreckage from the objects, but that they expected all three to be unrelated to surveillance efforts.

“The intelligence community is considering as a leading explanation that these could just be balloons tied to some commercial or benign purpose,” said White House national security spokesman John Kirby. No country or private company has come forward to claim any of the objects, Kirby said. They do not appear to have been operated by the U.S. government.

Still unaddressed are questions about the original balloon, including what spying capabilities it had and whether it was transmitting signals as it flew over sensitive military sites in the United States. It was believed by American intelligence to have initially been on a track toward the U.S. territory of Guam, according to a U.S. official.

The U.S. tracked it for several days after it left China, said the official, who spoke to The Associated Press on condition of anonymity to discuss sensitive intelligence. It appears to have been blown off its initial trajectory and ultimately flew over the continental U.S., the official said.

Balloons and other unidentified objects have been previously spotted over Guam, a strategic hub for the U.S. Navy and Air Force in the western Pacific.

It’s unclear how much control China retained over the balloon once it veered from its original trajectory. A second U.S. official said the balloon could have been externally maneuvered or directed to loiter over a specific target, but it’s unclear whether Chinese forces did so.

After the balloon was shot down, the White House revealed that such balloons had traversed U.S. territory at least three times during President Donald Trump’s administration unknown to Trump or his aides — and that others have flown over dozens of nations across five continents. Kirby emphasized Monday that they were only detected by the Biden administration.