President Biden sent a warning to the presidents of China and Russia during his Memorial Day address on Sunday.

"I had a long conversation for two hours recently with [Chinese] President Xi [Jinping], making it clear to him we could do nothing but speak out for human rights around the world because that's who we are," Biden said. "I'll be meeting with [Russian] President [Vladimir] Putin in a couple weeks in Geneva making it clear that we will not stand by and let him abuse those rights."

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Biden spoke at a Memorial Day service in Delaware on Sunday morning, where he offered comfort to the families of fallen service members and paid tribute to his late son Beau Biden, who served in the Iraq War. 

"It's also an important tradition in our family. As many of you know, this is a hard day for us. Six years ago today … I lost my son. In the first year of his passing back in 2016, Gen. [Frank] Vavala did a great honor in inviting us to a ceremony renaming the Delaware National Guard headquarters in Beau's honor."

President Joe Biden speaks with priests as he departs after attending Mass at St. Joseph on the Brandywine Catholic Church, Sunday, May 30, 2021, in Wilmington, Del. (AP Photo/Patrick Semansky)

"We're honored, but it's a tough day, brings back everything," Biden continued. "So I can't thank you enough for your continued service to the country and your sons, your daughters, they live on in your hearts and in their children as well. And we have to carry on without them. But I know how hard it is for you. Beau didn't die in the line of duty, but he was serving in Delaware National Guard unit in Iraq for a year. That was one of the proudest things he did in his life. So thank you for allowing us to grieve together today."

Beau Biden, the former attorney general of Delaware, died in 2015 from cancer. The president has previously suggested that Beau Biden's cancer could have been linked to toxins he was exposed to through military burn pits while serving in the Iraq War.

This is President Biden's first Memorial Day weekend as commander-in-chief.

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He brought up his issues with Chinese leaders as his administration refuses to commit to punishing China should the coronavirus lab leak theory be proven true.

"We haven't ruled out anything yet," principal deputy press secretary Karine Jean-Pierre told reporters during Wednesday's press briefing when asked whether the virus had emerged in a manner that was "deliberate or not an accident."

"Would the president seek to punish China?" Fox News’ Peter Doocy asked Jean-Pierre.

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"We're not going to go there just yet," Jean-Pierre replied, "We have to go through the 90-day review. And once we have the 90-day review, will we be able to reassess."  

Biden previously said he had asked the intelligence community to "redouble their efforts" to "bring us closer to a definitive conclusion" and get back to him within 90 days. 

Fox News' Lucas Y. Tomlinson, Morgan Phillips and The Associated Press contributed to this report.