MANILA — Philippine and Chinese officials on Wednesday called for a diplomatic solution to a naval standoff in the South China Sea, while insisting that they would defend their territorial claims in the region.

“If the Philippines is challenged, we are prepared to secure our sovereignty,” Albert F. del Rosario, the Philippine foreign secretary, said at a news conference as a Philippine frigate and two Chinese ships positioned themselves near disputed islands in the South China Sea. The Chinese Embassy in Manila issued a statement reaffirming its claim to sovereignty over the islands and said that the Philippine Navy was harassing its fishing vessels in the area.

The standoff comes at a time of increasing assertiveness by China in its claims to the South China Sea waters around the Philippines. The dispute intensified after the Philippines announced in February that it would invite foreign energy companies to explore for oil and gas in the waters west of Palawan Province, and adjacent to the Spratly Islands.

The Philippines, an ally of the United States, has become a particular target of China’s anger in the South China Sea disputes. Some analysts speculate that Beijing’s harsher tone could be a tit-for-tat after Secretary of State Hillary Rodham Clinton stood on the deck of an American warship last November in Manila Bay and reaffirmed the military alliance between the Philippines and the United States.