China announced on Saturday the two lighthouses have begun operating on Huayang Reef, which is part of a disputed island chain also claimed by Taiwan, Malaysia, Vietnam, Brunei and the Philippines.

The country also said it plans to continue building on the islands, despite growing friction with its neighbors in the region, as well as the United Sates.

Xinhua News Agency said the Transportation Ministry held a ceremony on the Spratly Islands -- which China calls the Nansha Islands -- to celebrate the completion of the 50-meter-high (164-foot-high) lighthouses.

"Next, China will continue to build other civil facilities on occupied island reefs in the Nansha Islands," said a foreign ministry spokeswoman in an online statement.

Bone of contention

Though mostly barren, the islands are located near one of the world's busiest sea lanes and have been at the center of ongoing disputes between Beijing, Washington and other regional governments. China lays claim to much of the South China Sea, a fact that has caused tensions between it and the United States, which has insisted China stop its construction there.

US President Barack Obama has repeatedly backed Japan, South Korea and the Philippines in their ongoing territorial disputes with China, and one US military official said the Pentagon would be ready to respond to defend its allies' sovereignty.

On Friday, China's Foreign Ministry expressed "serious concern" that Washington might send ships within the islands' 12-nautical-mile limit.

blc/tj (AP, AFP, dpa)