HONG KONG — The Chinese government Saturday claimed the right to identify, monitor and possibly take military action against aircraft that enter a newly declared “air-defense identification zone,” which covers sea and islands also claimed by Japan and threatens to escalate a tense dispute over some of the territory.

The move appeared to be another step in China’s efforts to intensify pressure on Japan over the Japanese-controlled islands in the East China Sea that are at the heart of the dispute. The islands are known as the Senkaku in Japan and the Diaoyu in China. South Korea and Taiwan also claim the barren, uninhabited islands.

The declaration, from a Ministry of National Defense spokesman, Col. Yang Yujun, accompanied the ministry’s release of a map, geographic coordinates and rules in Chinese and English that said: “China’s armed forces will take defensive emergency measures to respond to aircraft that do not cooperate in identification or refuse to follow orders.”

Later Saturday, China’s air force said it had dispatched its first planes, including fighter jets, to enforce the rules. Soon afterward, Japan scrambled its own fighter jets, Reuters reported, citing the Japanese Defense Ministry. A spokesman for the ministry said two Chinese reconnaissance planes had flown within about 25 miles of what Japan considers its airspace, Reuters said.

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The Chinese announcement followed months of increasing tension over the uninhabited islands as China appeared to be moving to establish its claim to them, including more frequent patrols by ships around the islands. Those patrols have led to cat-and-mouse games between Chinese and Japanese ships near the islands.

China’s new claim to the airspace near the islands could prove particularly problematic. Japan has scrambled fighter jets in the past when China has sent a plane, and possibly a drone, to the area, to ensure they were not entering what Japan considers its airspace.

As the potential for a miscalculation that leads to conflict has increased, the United States has become worried that, as an ally of Japan, it could be dragged into any conflict with China.

Tomohiko Taniguchi, a counselor in the office of Prime Minister Shinzo Abe, of Japan, said the new air-defense zone “potentially escalated the danger of accidental collisions between the Chinese military and the U.S. and Japanese counterparts.” The Japanese Foreign Ministry said the government had lodged a “serious protest” with China over the move.

Yang said the declaration of the air zone was not aimed at any particular country, and that it would not impede the freedom of commercial flight over the East China Sea. But his words left little doubt the move could be used against the Japanese government and military aircraft.

The Japanese Foreign Ministry said the government had lodged a “serious protest” with China over the move.

U.S. Secretary of State John Kerry said the U.S. was “deeply concerned” about China’s announcement and urged China not to implement its threat of military action.