President Joe Biden is preparing a speech about a Chinese balloon that was shot down at a high altitude and three other objects that were also shot down by American fighter jets. Lawmakers have demanded more information about these incidents, which have left many Americans perplexed, according to sources.

The remarks, which could be made as early as Thursday, were predicted by two sources who requested anonymity. They come amid claims that the purported surveillance balloon that was shot down on February 4 after crossing the continental US had been on a course that would have taken it over Guam and Hawaii, but that trajectory was altered by prevailing winds and instead caused it to pass over the other islands.

The balloon incident prompted U.S. Secretary of State Antony Blinken to postpone a planned visit to Beijing, where both sides had sought to stabilize already fraught relations.

Blinken’s scheduled attendance at the Munich Security Conference this weekend has raised speculation that he could meet China’s top diplomat Wang Yi there.

Biden has made few public comments about the situation and has been under pressure from critics to speak more extensively about the spate of flyovers. The timing of his speech is unclear, but Biden, 80, was scheduled on Thursday morning to have a physical examination at Walter Reed hospital.

John Bolton, a national security advisor during the Trump administration, said on Twitter that he had been briefed on Wednesday by the U.S. intelligence community and remained “profoundly troubled about the Biden Administration’s handling of these potential national-security threats,” citing what he called its “changing story line.”

The Washington Post reported on Tuesday that U.S. military and intelligence agencies tracked the balloon from when it lifted off from China’s southern island province of Hainan.

It was shot down by U.S. fighter jets off the coast of South Carolina, and American lawmakers have slammed the administration for letting it first drift across the country, including near sensitive military bases.

Asked about Biden’s expected remarks, a spokesman for China’s foreign ministry on Thursday once again referred to the downed balloon as an “unmanned civilian airship,” and said its flight into United States airspace was an “isolated” incident.

The U.S. “should be willing to meet China in the middle, manage differences and appropriately handle isolated, unexpected incidents to avoid misunderstandings and misjudgments; and promote the return of U.S.-China relations to a healthy and stable development track,” spokesman Wang Wenbin told reporters at a regular briefing.

Beijing had criticized Washington for overreacting by shooting down the balloon, and warned of “countermeasures against relevant U.S. entities that undermine China’s sovereignty and security.”

On Thursday, China put Lockheed Martin Corp and a unit of Raytheon Technologies Corp on an “unreliable entities list” over arms sales to Taiwan, banning them from imports and exports related to China in its latest sanctions against the U.S. companies.

Since an American fighter jet shot down the 200-foot (60-meter) Chinese balloon, three other objects have been downed over hard-to-reach areas – two in the frozen North and one whose debris plummeted into Lake Huron. White House national security spokesman John Kirby has said the United States still had no firm grasp on the origin of those three objects.

Biden has asked national security adviser Jake Sullivan to preside over a task force of related agencies to come up with guidelines on how to address unidentified objects in future.

It is supposed to come up with guidelines this week on what circumstances should be considered before shooting down an unidentified object.