MANILA, July 21 (Reuters) - The Philippines and China have "reached an understanding on the provisional arrangement" for resupply missions to a beached Filipino naval ship in the South China Sea, Manila's foreign ministry said in a statement on Sunday.

The Department of Foreign Affairs (DFA) did not provide details on the arrangement for the Philippines' resupply missions to the Sierra Madre on the Second Thomas Shoal.

But it said it followed "frank and constructive discussions" between the two sides at the Bilateral Consultation Mechanism earlier this month.

"Both sides continue to recognize the need to de-escalate the situation in the South China Sea and manage differences through dialogue and consultation and agree that the agreement will not prejudice each other’s positions in the South China Sea," the DFA said.

The Chinese foreign ministry confirmed the "temporary arrangement" with the two sides agreeing to jointly manage maritime differences and de-escalate the situation in the South China Sea.

"The Chinese side still demands that the Philippine side tow away the ship and restore the original status of (Second Thomas Shoal) as if it were unmanned and without facilities," a spokesperson said in a statement released early on Monday.

Manila deliberately beached the Philippine naval ship in 1999 to reinforce its claims over disputed waters around the shoal and it has since maintained a small contingent of sailors.

"If the Philippines needs to provide supplies to the ship's occupants before the Philippines tows away the beached warship, the Chinese side is willing to allow the Philippine side to carry out the transportation and replenishment on humanitarian grounds," the spokesperson said.

China still stood firm over its territorial claims regarding the disputed waters.

"If the Philippines transports a large amount of building materials to the ship and tries to build fixed facilities and permanent outposts, China will never accept it and will resolutely block it in accordance with laws and regulations, so as to safeguard China's sovereignty," the spokesperson added.

Philippine security officials also said on Sunday they will carry out the resupply missions on their own despite an offer from the United States for help.

White House National Security Adviser Jake Sullivan said on Friday the U.S. "will do what is necessary" to ensure its treaty ally can resupply the Sierra Madre on the Second Thomas Shoal.

Sullivan's Filipino counterpart, Eduardo Ano, said the resupply will remain "a pure Philippine operation".

"There is no need at this time for any direct involvement of U.S. forces in RORE (resupply) mission," Ano said in a statement.

Reuters previously reported that the Philippines turned down offers from the U.S. to assist its operations in the South China Sea.

Tensions in the disputed waterway have boiled over into violence in the past year, with a Filipino soldier losing a finger last month in a clash that Manila described as an "intentional-high speed ramming" by the China Coast Guard.

The Philippine military's spokesperson said in a separate statement on Sunday the Philippines "will exhaust all means before seeking foreign intervention" in its resupply missions.

Manila and Washington are bound by the 1951 Mutual Defense Treaty, a pact that can be invoked in case of an armed attack against Philippine forces, public vessels or aircraft in the South China Sea. U.S. officials including President Joe Biden have affirmed its "ironclad" commitment to aid the Philippines.

China claims nearly all of the South China Sea, overlapping maritime claims of the Philippines, Vietnam, Malaysia and Brunei. In 2016, a Hague-based tribunal said China's claims had no legal basis, a decision Beijing has rejected.

Photo from Reuters