Visitors to the Chinese military museum look at remains of U.S.-made Taiwanese reconnaissance planes, at left, shot down by the Chinese in the 1960s, and a Chinese fighter jet Saturday in Beijing. China angrily summoned the U.S. ambassador on Saturday and warned that a plan to sell .4 billion in arms to Taiwan would harm already strained ties. One Chinese expert said the sale would give Beijing a “fair and proper reason” to accelerate weapons testing.

Beijing ? China’s foreign minister warned that U.S. plans to sell $6.4 billion of arms to Taiwan will harm Chinese efforts to unify peacefully with the island, the ministry said today, after China suspended U.S. military exchanges and threatened unprecedented sanctions against American defense companies.

Foreign Minister Yang Jiechi said the planned weapons sales to self-governing Taiwan, which Beijing claims as its territory, were a “crude interference in China’s internal affairs” and would hurt its national security.

Beijing’s strong response to Friday’s U.S. announcement of the weapons sales, while not entirely unexpected, was swift and indicated that it plans to put up a greater challenge than usual as it deals with the most sensitive topic in U.S.-China relations.

“This is the strongest reaction we’ve seen so far in recent years,” said Stephanie T. Kleine-Ahlbrandt, northeast Asia project director for the International Crisis Group. “China is really looking to see what kind of reaction it’s going to receive” from President Barack Obama, she said.

China’s Defense Ministry said the arms sales would cause “severe harm” to overall U.S.-China cooperation. Vice ministerial-level talks on arms control and strategic security were postponed.

Defense Ministry spokesman Huang Xueping said the Chinese military would fight any move to hurt the country’s sovereignty.

“We will never give in or compromise in this issue,” Huang said in a statement.

In comments made during a visit to Cyprus on Saturday, Foreign Minister Yang urged Washington to respect China’s interests and revoke the arms sale decision immediately to avoid undermining bilateral relations, the Foreign Ministry said. He said the U.S. sales “jeopardized China’s national security and China’s peaceful reunification efforts.”

The warning came as the U.S. seeks Beijing’s help on issues including the global financial crisis and nuclear standoffs in North Korea and Iran. Tensions were already high after recent U.S. comments on Internet freedom and a dispute between Google and China, as well as Obama’s plan to meet with Tibetan spiritual leader the Dalai Lama this year.

China’s Vice Foreign Minister He Yafei told U.S. Ambassador Jon Huntsman that the sales of Black Hawk helicopters, Patriot Advanced Capability-3 missiles and other weapons to Taiwan would “cause consequences that both sides are unwilling to see,” the ministry said.

The ministry also threatened sanctions against U.S. companies involved in the arms sales, which hasn’t happened in past sales to Taiwan.

“Our action regarding Taiwan reinforces our commitment to stability in the region,” U.S. State Department spokesman P.J. Crowley said in Washington on Saturday. “We know China has a different view. Given our broad relationship with China, we will manage this issue as we have in the past.”