The US must sanction Hong Kong judges and prosecutors, prevent its chief executive from attending a San Francisco economic summit and close the Hong Kong Trade and Economic Offices in the US, witnesses told a congressional advisory group on Thursday – measures that the panel’s leader, Representative Chris Smith, vowed to act on.

The hearing was titled “One City, Two Legal Systems: Political Prisoners and the Erosion of Rule of Law in Hong Kong” and hosted by the Congressional-Executive Commission on China, which advises lawmakers and the executive branch on human rights and the rule of law in China.

One of the four witnesses was Sebastien Lai, the son of imprisoned media tycoon Jimmy Lai Chee-ying, who called on the US “to do all it can” to secure his father’s release.