China on Saturday expressed firm opposition to the U.S. State Department's approval of an arms sale to China's Taiwan region, and urged the U.S. to earnestly abide by the one-China principle, according to a spokesperson of the Chinese Embassy in Washington.

China will resolutely take legitimate and necessary counter-measures in light of the development of the situation, spokesperson Liu Pengyu tweeted.

This came after the Pentagon's Defense Security Cooperation Agency announced on Friday that the U.S. State Department had approved the sale of 60 anti-ship missiles, 100 air-to-air missiles and contractor logistics support to Taiwan in a deal valued at $1.1 billion.

Noting that Taiwan is an inalienable part of China's territory, the spokesperson said that the United States is interfering in China's internal affairs and undermining China's sovereignty and security interests by selling arms to the Taiwan region.

The move runs counter to international law and the basic principles of international relations, and violates the one-China principle and the provisions of the three China-U.S. joint communiques, particularly the August 17 communique, Liu stressed.

He also pointed out that the move sends wrong signals to "Taiwan independence" separatist forces, and severely jeopardizes China-U.S. relations and peace and stability across the Taiwan Straits.

The spokesperson urged the U.S. side to honor its commitments, earnestly abide by the one-China principle and the three China-U.S. joint communiques, stop arms sales to and military interactions with Taiwan, and immediately revoke relevant arms sales to Taiwan, lest more damage be dealt to China-U.S. relations and peace and stability across the Taiwan Straits.