BEIJING -- China on Monday confirmed that coast guard vessels had driven away two Philippine ships from the Ren'ai Reef off China's Nansha Islands.

Chinese Foreign Ministry spokesman Qin Gang said coast guard vessels, patrolling the Ren'ai Reef, identified two ships loaded with construction materials and carrying the flags of the Philippines, approaching the reef on Sunday.

Having been warned by the Chinese vessels, the two Philippine ships left the reef, referred to as "Ayungin Shoal" by the Philippines, on Sunday afternoon, according to Qin.

"China has indisputable sovereignty over the Nansha Islands and their adjacent waters including the Ren'ai Reef," said the spokesman.

Qin recalled how a Philippine warship had illegally grounded on the Ren'ai Reef in 1999, claiming it had been stranded. Since then, China has repeatedly demanded the Philippines retrieve the warship, but all requests have been ignored and with "technical reasons" cited for the failure to do so, Qin said.

This time, again the Philippine side attempted to start construction on the reef, he said. "The moves infringed China's sovereignty and violated the spirit of the Declaration on the Conduct of the Parties in the South China Sea."

China had no choice but to respond to the Philippines' moves, he said.