HAIKOU, China -- New rules announced by a Chinese province last week to allow interceptions of ships in the South China Sea are raising concerns in the region, and in Washington, that simmering disputes with Southeast Asian countries over the waters will escalate.
The move by Hainan province, which administers the sea for China, is being seen by some outside analysts as another step in the country's bid to solidify claims to much of the sea, which includes crucial international shipping lanes through which more than a third of global trade is carried.
As foreign governments scrambled for clarification of the rules, which appeared vague and open to interpretation, a top Chinese policymaker on matters related to the South China Sea tried to calm worries inspired by the announcement. Wu Shicun, the director general of the foreign affairs office of Hainan province, said Saturday that Chinese ships would be allowed to search and repel foreign ships only if they were engaged in illegal activities and only if the ships were within the 12-nautical-mile zone surrounding islands that China claims.
The laws, passed by the provincial legislature, come less than a month after China's new leader, Xi Jinping, took office, and as the country remains embroiled in a serious dispute with Japan in the East China Sea over islands known in China as Diaoyu and as Senkaku in Japan.
The laws appear to have little to do with Mr. Xi directly, but they reinforce the fears that China, now the owner of an aircraft carrier and a growing navy, is plowing ahead with plans to enforce its claims that it has sovereign rights over much of the sea, which includes dozens of islands that other countries say are theirs. And top Chinese officials have not yet clarified their intent, leaving room for speculation.
If China were to enforce these new rules fully beyond the 12-nautical-mile zones, naval experts say, at stake would be freedom of navigation, a principle that benefits not only the United States and other Western powers but also China, a big importer of Middle Eastern oil.
As in many aspects of the increasingly heated arguments over China and its role in the South China Sea, the exact meaning of the new regulations has not been explained yet by top Chinese officials. An incomplete list of the laws passed in Hainan, which is responsible for administering China's South China Sea claims, was announced in the state-run news agency, Xinhua, last week.
In an interview Saturday, Mr. Wu said the new regulations applied to all of the hundreds of islands scattered across the sea, and their surrounding waters. That includes islands claimed by several other countries, including Vietnam and the Philippines.
"It covers all the land features inside the nine-dash line and adjacent waters," Mr. Wu said. The nine-dash line refers to a map that China drew up in the late 1940s that demarcates its territorial claims -- about 80 percent of the South China Sea, whose seabed is believed to be rich in oil and natural gas.
That map, which outraged some neighboring countries when China recently placed the nine-dash map on its new passports, forms the basis for China's current claims.
Mr. Wu, who also heads a government-sponsored institute devoted to the study of the South China Sea and is one of China's leading experts on the sea, said the immediate intention of the new laws was to deal with what he called illegal Vietnamese fishing vessels that operate in the waters around Yongxing Island where China recently established an expanded army garrison.
The island, which has a long airstrip, is part of a group known internationally as the Paracels that is also claimed by Vietnam. China is using Yongxing Island as a kind of forward presence in a bid for more control of the South China Sea, neighboring countries say.
The Philippines, an ally of the United States and one of the most vociferous critics of China's claims in the South China Sea, reacted strongly to the new rules.
In a statement, the Foreign Ministry in Manila said Saturday, "This planned action by China is illegal and will validate the continuous and repeated pronouncements by the Philippines that China's claim of indisputable sovereignty over virtually the entire South China Sea is not only an excessive claim but a threat to all countries."
On Saturday the Obama administration, in an effort not to escalate the situation, only obliquely criticized the Chinese action. "All concerned parties should avoid provocative unilateral actions that raise tensions and undermine the prospects for a diplomatic or other peaceful resolution," said Peter Velasco, a State Department spokesman.
At a summit of Asian leaders in Phnom Penh, Cambodia, last month President Barack Obama raised the issue of the South China Sea in a meeting with China's Premier Wen Jiabao, senior administration officials said. Mr. Obama asked the Chinese to resolve disputes peacefully, and to allow freedom of navigation, they said.