Manila, Philippines - The Philippines' military said on Tuesday that Chinese boats illegally "seized" food and medicine supplies airdropped to a Filipino outpost in the South China Sea.

The incident allegedly happened on May 19 at Second Thomas Shoal in the Spratly Islands, where Filipino troops are garrisoned on a grounded navy vessel, in a bid to assert Manila's claims to the waters.

Military spokespeople accused China of "aggressive and unprovoked interference" when two Chinese rigid-hulled inflatable boats allegedly came within 30 feet of the Sierra Madre vessel and seized an airdropped package meant for Filipino troops.

According to the Filipino military, it was the first time that supplies had been seized by the Chinese.

According to Filipino military chief General Romeo Brawner, "This action of getting or confiscating our supplies is illegal... You're not supposed to confiscate the supplies of another country, even in war."

Chinese personnel on board the boats later dumped the items in the water, Philippine Navy spokesperson for the West Philippine Sea Commodore Roy Vincent Trinidad said. It was not clear if the vessels belonged to the Chinese coast guard or navy.

Nearby Filipino troops managed to retrieve most of the items that had been airdropped by the military, but the incident has strained diplomatic relations between Manila and Beijing.

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Tensions have been particularly high of late, following US-Filipino war games which saw joint military drills simulate mock assaults on Chinese forces. The maneuvers were decried as "provocations" by Beijing.

After the comments by Filipino spokespeople, Chinese foreign ministry spokesperson Mao Ning told reporters that Manila should "stop making trouble" and respect Chinese sovereignty.

According to the Chinese, the c is Chinese property. The reef is located more than 600 miles from the nearest Chinese landmass and less than 120 miles from the Philippines.

"The Philippine side has also repeatedly provoked and intensified conflicts, escalating the situation. This is unacceptable to us," Mao Ning said.