Photo: Xinhua

A military spokesperson said that the People's Liberation Army will stay on high alert and take all necessary measures to protect national sovereignty and security and safeguard peace and stability in the South China Sea, after two US ships illegally entered the area.

Senior Colonel Li Huamin, a spokesperson of the Southern Theater Command of the People's Liberation Army, made the remarks after they discovered US guided-missile destroyers Preble and Chung Hoon traveling close to the Nansha Islands on Monday.

The command had identified and warned the ships to leave in accordance with laws, Li said in a statement released on the command's WeChat account on Monday afternoon.

China owns indisputable sovereignty over the Nansha Islands and their adjacent waters, Li noted.

Geng Shuang, a spokesperson of the Chinese Foreign Ministry, expressed China's strong discontent and firm opposition to the US destroyers' behavior at a routine press conference on Monday. The behavior violated China's sovereignty, disturbed regional peace and stability, he noted.

The two destroyers traveled within 12 nautical miles of the Nancun and Chigua reefs in the Nansha Islands, according to Geng.

"The situation in the South China Sea is improving thanks to the efforts of China and ASEANcountries," Geng said, urging the US to stop such provocative operations.

The operations are the latest of the US to threaten China's sovereignty in the South China Sea under the name of freedom of navigation, which experts said is just "an excuse for the US to stir up tensions in the region and contain China."

"The US' excuse of freedom of navigation does not stand because international law never allowed US warships to freely enter another country's territorial waters," Zhang Junshe, a senior research fellow at the PLA Naval Military Studies Research Institute, told the Global Times on Monday.

"As you can see, the situation in the South China Sea has already stabilized. Countries directly involved, including the Philippines, all agreed to peacefully solve the problems through dialogue and negotiations, and these countries are now focusing on economic cooperation," Zhang noted.

Countries like Malaysia, Vietnam, the Philippines and Brunei sent naval vessels to China in April, joining the celebrations of the PLA Navy's 70th anniversary. Following the celebrations, China held a joint naval exercise with the Southeast Asian countries in Qingdao, East China's Shandong Province, from April 24-26.

These show that countries around the South China Sea want peace and stability in the region, which is being sabotaged by US actions, according to Zhang.