China launched military exercises around Taiwan on Saturday as a “serious warning” to separatist forces, in an angry but long-awaited response to Vice President William Lai’s visit to the United States. Lai, the favorite to become Taiwan’s president in the January elections, returned from the United States on Friday. Officially, he only made a stopover on his round trip to Paraguay, but he made speeches during his stay in the United States.

China considers Taiwan its own territory, despite strong objections from the island’s government.

The People’s Liberation Army Command, which is responsible for the area around Taiwan, said in a brief statement that it was conducting joint combat readiness air and naval patrols around the island.

Taiwan’s Defense Ministry said it had detected 42 Chinese planes and eight ships taking part in maneuvers around the island since Saturday morning and had deployed ships and planes in response.

Twenty-six Chinese planes crossed the 100 km-wide median line of the Taiwan Strait or areas beyond each end of the line, the ministry said in a statement. For decades, the line has served as an unofficial barrier between the two armies.

The Chinese military said it was conducting joint naval and air force exercises and training, focusing on ship-aircraft coordination and seizure control, to test the “actual combat capabilities” of the forces. “This is a serious warning against Taiwanese separatist forces colluding with outside forces to provoke,” he said.

He released video footage allegedly taken on Saturday showing J-16 and J-10 fighter jets and a naval destroyer on patrol. In text accompanying the images, set to a thunderous orchestral score, the exercises were said to “test the actual combat capabilities of joint operations forces in the theater of operations.”

The deployed equipment included destroyers, frigates and fast missile boats, as well as fighters, early warning and jamming planes that “were assembled in a predetermined area,” he said, without elaborating. The forces carried out an “omnidirectional encirclement of the island,” the command said.

The Taiwanese government strongly condemned the moves, with the Defense Ministry saying it had the necessary capacity, determination and confidence to ensure national security.

The government’s Mainland Affairs Council, which makes China’s Taiwan policy, urged Beijing to end its intimidation and start talks, saying the people of Taiwan were determined to defend themselves and would never succumb to threats of force.

“The ROC Taiwan is a sovereign country and has the legitimate and legal right to maintain normal diplomatic interactions with friendly countries,” it added in a statement, using the island’s formal name.

Taiwan’s Defense Ministry released a short undated video showing Taiwanese forces maneuvering at sea, on city streets and in the countryside. Also set to orchestral music, the video was titled “Firmly Defend National Sovereignty and Protect Democratic Freedom and People’s Security!”

Hours before the drills, the President of the United States, Joe Biden, and the leaders of South Korea and Japan agreed at Camp David to deepen defense and economic cooperation, while reaffirming “the importance of peace and stability across the Taiwan Strait as an indispensable element of security and prosperity in the international community.”