Trump administration: Jimmy Lai's arrest marks Beijing's "latest violation" on Hong Kong

National Security Adviser Robert O'Brien said in a statement Monday night the Trump administration is "deeply troubled" by the arrest of Hong Kong pro-democracy activist Jimmy Lai on suspicion of "collusion with foreign powers."

Why it matters: The arrest Monday of the most prominent person under the new national security law that gives Beijing more powers over the former British colony comes amid heightened tensions between the U.S. and China.

• The U.S. has sanctioned Chinese officials, including Hong Kong leader Carrie Lam, over the move, which strips key aspects of the territory's autonomy. China hit back on Monday, sanctioning Sens. Marco Rubio and Ted Cruz, along with nine other American officials.

Details: Lai has been bailed, per the BBC. The 72-year-old's son was also arrested, Lai's pro-democracy newspaper the Apple Daily reports

• Mark Simon, an executive at the tycoon's media firm Next Digital, tweeted that police had gone to Lai's home after issuing search warrants before heading to Apple Daily's newsroom to conduct a search.
• Hong Kong police said in a statement Monday they searched a building in Tseung Kwan O, where Apple Daily's headquarters are located. They said they had arrested seven people on suspicion of breaching the national security law.
• "Offences include collusion with a foreign country/external elements to endanger national security," the police added.

What they're saying: "These reported arrests, following the recent action by the Hong Kong government to unjustly disqualify candidates and postpone the Legislative Council elections, are the latest violations of Beijing’s commitments to the Hong Kong people and the world," O'Brien said.

"These arrests are also a clear effort to intimidate pro-democracy and political opposition figures and suppress Hong Kong’s free and independent media, which have played  key roles in the city’s character and success."

Of note: Lai was among a group of activists arrested earlier this year on charges of holding illegal assemblies in August and October related to the massive pro-democracy protests that swept the Asian financial hub last year.

• When the national security law was imposed by Chinese lawmakers in June, Lai told the BBC in response that it "spells the death knell for Hong Kong."

Go deeper: With new security law, China outlaws global activism

Editor's note: This article has been updated with new details throughout.