US Pacific Fleet spokesman Lieutenant Clint Ramsden said Thursday the patrols were part of a "routine presence" but that he could not go into operational or tactical details.

"All of these patrols are conducted in accordance with international law and all are consistent with routine Pacific Fleet presence throughout the Western Pacific."

The US destroyers were conducting patrols within 14 to 20 nautical miles (25 to 37 kilometers) of Scarborough Shoal and the Spratly Islands near the Philippines.

On Wednesday, Chinese Foreign Minister Wang Yi warned US Secretary of State John Kerry that Washington must not harm Beijing's sovereignty and security in the South China Sea.

The patrols come ahead of a ruling by the International Court of Justice in the Dutch city of The Hague about the dispute between China and the Philippines over the South China Sea.

China has refused to participate in the case and vowed to ignore the rulings which the US insists are binding and an important test of Beijing's willingness to adhere to international law.

The South China Sea has become a source of tension between the US, China and some regional countries who are seeking control of trade routes and mineral deposits.

China claims nearly all of the South China Sea, despite partial counterclaims by Brunei, Malaysia, Taiwan, Vietnam and the Philippines. China is also locked in disputes with Japan and South Korea over the East China Sea.

Aside from challenging China's sovereignty claims politically, the US has also on numerous occasions sent warships near Chinese artificial islands in the disputed waters.

China has repeatedly criticized US military presence in the region and suspects the military drills are part of efforts to contain Beijing.

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