MANILA, Philippines: The contested South China Seas again heated up this week as Chinese coast guard ships blocked two Philippines boats, then shot water at them using water cannons, as they carried supplies to Filipino troops in a disputed South China Sea shoal.

The Chinese actions resulted in Manila ordering Beijing's ships to retreat, and warned China that Filipino supply vessels are protected by a mutual defense treaty with the United States.

Philippine Foreign Secretary Teodoro Locsin Jr. reported that no injuries occurred, though the two supply ships were not able to carry out their mission to provide food to Filipino forces occupying Second Thomas Shoal, located in the Philippines' internationally recognized economic zone.

Also, Locsin said in a tweet that the actions by the Chinese coast guard ships were illegal and urged the ships "to take heed and back off."

This was yet another flare-up inside the territorial waterway, in which China, the Philippines, Vietnam, Malaysia, Brunei and Taiwan have voiced claims. In recent years China has said the entire South China Sea falls within its territories. It has also transformed seven shoals into island bases, complete with missiles, which increased regional tensions.

Further, the Philippine government conveyed to China, "our outrage, condemnation and protest of the incident," Locsin said, noting, "This failure to exercise self-restraint threatens the special relationship between the Philippines and China."

In Beijing, however, Chinese Foreign Ministry spokesperson Zhao Lijian claimed China had acted to uphold its sovereignty, after the Philippines ships entered Chinese waters without permission.

In recent weeks, China has increased the number of surveillance ships in the disputed waters around the Philippines.

In response, Esperson said, "We will continue the resupply and we do not have to ask the permission of anybody, because that is within our territory."

In 1999, the Philippines deliberately ran aground a World War II warship, the BRP Sierra Madre, onto the shoal to reinforce its territorial claim and provide shelter to a contingent of Filipino marines.

Though the Sierra Madre is today a shipwreck, the Philippine military has not decommissioned it.

In international terms, the ship remains an extension of the government and any attack on the ship is the same an assault against the Philippines.

Also, Philippines Navy ship LT 57 with Philippines troops aboard is stationed off Second Thomas Shoal, locally known as Ayungin Shoal, in the South China Sea.

Meanwhile, the United States continues to patrol the region with its ships and aircraft, in a bid to ensure that the seas remain open to all shipping, including ships from the Philippines.

China has repeatedly warned the U.S. to stay out of the disputed waters.