BEIJING — China on Thursday imposed trade and investment sanctions on U.S. military contractors Lockheed Martin and Raytheon for supplying weapons to Taiwan, stepping up efforts to isolate the island democracy claimed by the ruling Communist Party as part of its territory.

The companies are barred from importing goods into China or making new investments in the country, the Ministry of Commerce announced.

It wasn’t clear what impact the penalties might have on Lockheed Martin or Raytheon. The United States bars most sales of weapons- …