BEIJING/TOKYO - Chinese state media blasted the United States on Monday for a planned $6.4 billion arms package for Taiwan, while a US official said Washington was committed to helping the island defend itself. The arms sales, the latest in a series but the first by the Obama administration, has added to a litany of bilateral strains between the world's biggest and third-biggest economies, including the value of China's currency, trade protectionism, Internet freedoms and Tibet. The official China Daily said US weapons sales to the self-ruled island, which China claims as its own, "inevitably cast a long shadow on Sino-US relations." "China's response, no matter how vehement, is justified. No country worthy of respect can sit idle while its national security is endangered and core interests damaged," the English-language newspaper said in an editorial. The United States switched diplomatic recognition from Taipei to Beijing in 1979, recognizing "one China," and says it wants the two sides to settle their differences peacefully. The United States remains Taiwan's biggest backer and is obliged by the 1979 Taiwan Relations Act to help in the island's defense. US Assistant Secretary of Defense for the Asia-Pacific Wallace Gregson said Washington aimed to maintain cooperative, cordial relations with China but would not abandon Taiwan. "The United States is also obligated to ensure Taiwan's self-defense capability and the United States fully intends to meet every one of our obligations there and we will continue to do so into the future," he said in Tokyo.