Vietnam is verifying information that Philippine President Rodrigo Duterte had ordered troops to occupy uninhabited islands and shoals that the Philippines claims in the East Sea, the Vietnamese reference for the flashpoint South China Sea.

An aerial photo shows Thitu Island, part of the disputed Spratly group of islands, in the East Sea, the Vietnamese reference for the South China Sea. Photo: AFP

Also in a statement on Thursday, Duterte said he might visit Thitu (Pagasa) Island in the Spartly Archipelago, over which Vietnam claims sovereignty, on June 12 (the Philippines' Independence Day).

Le Thi Thu Hang, Vietnam’s foreign ministry spokesperson, said in a statement Sunday that Vietnam has sufficient evidence to prove its sovereignty over the Spartlys and the Paracel archipelago, another island chain in the Eat Sea.

Without permission from Vietnam, any action by other countries on the two island chains is illegal and invalid, she said.

Hang also stressed that Vietnam wants to settle all disputes in the East Sea via peaceful means in line with international law, urging parties concerned to refrain from actions that could further complicate the status quo in the already troubled waters. 

China, Malaysia, the Philippines, Taiwan, Brunei and Vietnam contest all or parts of the East Sea. This has led to confrontations between China and some of its neighbors over the strategic trade route.

On Friday, Philippine defense and military officials sought to clarify their president's comments.

The Philippines will upgrade existing facilities on its inhabited islands and reefs in the South China Sea and not occupy new territories, adhering to a 2002 informal code in the disputed waters, they said.

"The president's order was very crystal clear. Occupy only the existing areas that we claim," a navy commander, privy to development plans in the South China Sea, told Reuters on Friday.

"The Philippines is not allowed to do that, occupy new territories in the Spratly, based on the 2002 agreement," said the navy official.