WASHINGTON — 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 off the South Carolina coast 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 downing 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 Antony 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 road map 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 traveled 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.

Hours before his remarks, Biden had a routine medical checkup at Walter Reed National Military Medical Center, a keenly watched exam as the oldest president in history makes plans for an expected reelection campaign.

Biden, 80, was at the hospital in Bethesda, Maryland, for about three hours before leaving by helicopter shortly after noon for the White House. The White House was expected to release a letter later Thursday that would discuss the results.

“Well, everything really went well,” Biden told NBC News after the exam.