BEIJING (AP) -- China announced sanctions on six U.S. companies on Thursday as frictions continue to escalate in the countries' trade relations despite a highly anticipated meeting between U.S. President Donald Trump and Chinese leader Xi Jinping.

Three U.S. companies have been added to China's "unreliable entity list," effectively banning them from trade with China, according to a statement by the Commerce Ministry.

The ministry said the companies have "engaged in so-called military-technical cooperation with Taiwan, severely undermining China's national sovereignty, security and development interests."

The companies are unmanned vehicle maker Saronic Technologies, satellite technology company Aerkomm and subsea engineering firm Oceaneering International.

China sees self-ruled Taiwan as a breakaway province, to be annexed by force if necessary. In July, Beijing imposed export controls on eight enterprises tied to Taiwan's military.

Separately, three other U.S. companies were added to China's export control list, preventing them from receiving Chinese shipments of "dual use" items, with both military and civilian applications.

The companies are military shipbuilder Huntington Ingalls Industries, engineering and facilities manager Planate Management Group and intelligence firm Global Dimensions.

The three companies "endanger China's national security and interests," the Commerce Ministry said.

After a lengthy phone call with Xi last week, Trump said the two leaders would meet at a regional summit in South Korea at the end of October. Beijing and Washington say they want to iron out differences over trade, technology and the ownership of social media platform TikTok.