The United States has issued a warning to China that in case of an attack on the Philippines in the South China Sea, the country is committed to defending the island nation under a 70-year-old mutual defense treaty.

The comments were made by US Secretary of State Antony Blinken in a statement on Sunday.  The statement was issued to mark the fifth anniversary of an independent arbitration tribunal ruling. The ruling had rejected China’s territorial claims over the disputed sea and had sided with the Philippines.

“We also reaffirm that an armed attack on Philippine armed forces, public vessels, or aircraft in the South China Sea would invoke US mutual defense commitments under Article IV of the 1951 US-Philippines Mutual Defense Treaty,” CNN quoted Blinken as saying.

The Permanent Court of Arbitration had outrightly dismissed the Chinese claims to the South China Sea in 2016. The tribunal has also rebuked China for infringing on Philippine sovereignty by building islands in the country’s Exclusive Economic Zone (EEZ). China had rejected the ruling.

Blinken has also asked China to “take steps to reassure the international community that it is committed to the rules-based maritime order that respects the rights of all countries, big and small,” CNN reported.

Tensions have been at a high in the South China Sea this year, with the Philippines saying that China has deployed its maritime militia to intimidate its Coast Gaurd and fishing boats. The Chinese claims on the region are also contested by Brunei, Malaysia, Taiwan, and Vietnam.