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 China’s South China Sea claims, is being seen by some outside analysts as another step in the country’s bid to solidify its 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 policy maker 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 (though these were not defined) and only if the ships were within the 12-nautical-mile zone surrounding islands that China claims.