WASHINGTON — The Trump administration has blocked the websites of five major Chinese state-owned media outlets — including a YouTube-style video streaming site that some experts believe will become the Internet home of China’s Communist Party — from a key online protocol used by nearly 200 million computers, phones and televisions.

The move raises the stakes for China, which is using websites to spread its ideology and propaganda on a scale never before seen in a foreign country. It also comes ahead of what could be an increasingly significant election in China this year, and as Beijing is gearing up for a new round of military adventurism.

An administration official said U.S. law prohibits the Department of Homeland Security from having the websites, now called “Foreign Media Spies,” accessible under the Domain Name System, an Internet system that coordinates the transfer of websites from one place to another.

The department’s actions appear to represent a wholesale rejection of China’s efforts to control what gets posted online by undermining the way that people get to sites like China Central Television. Because of the Domain Name System’s system, about 700 million Americans, Europeans and people in other countries have no way of finding and accessing the websites.

Those that do are redirected to the sites through redirectors, rendering the websites inaccessible for Internet users. It has been reported in the news that Chinese hackers are trying to block access to the websites by using the internet anonymizing service Tor.