Early Wednesday morning, President Donald Trump tweeted that Hillary Clinton‘s emails were hacked by China and said, without citing evidence, the FBI and Justice Department would risk their credibility, calling it “a very big story.”

On Tuesday evening, the President posted a tweet, joking about Russia’s role in the hacking scheme, “Are they sure it wasn’t Russia (just kidding)?”

Trump provided no further details on where did he got the information but it appeared to stem back to a story by the right-wing website Daily Caller reporting that a Chinese-owned company in Washington hacked Clinton’s private server while she was secretary of state. The publication cited “two sources briefed on the matter.”

China denied the report in a statement, and said it “firmly oppose[s]” cyberattacks and the theft of state secrets.

“This isn’t the first time we’ve heard similar kinds of allegations,” Chinese Foreign Ministry spokeswoman Hua Chunying said at a daily news briefing. “China is a staunch defender of cybersecurity. We firmly oppose and crack down on any forms of internet attacks and the stealing of secrets.” China and the United States are currently in the midst of an escalating trade war.

U.S. intelligence agencies have said Russia orchestrated the hacking of Democratic emails to meddle with the 2016 presidential election. The Justice Department indicted 12 Russian intelligence officers in July on charges of hacking into Clinton’s presidential campaign and the Democratic Party.