Chinese Foreign Ministry spokesman Hong Lei said Tuesday that "it is illegal for any country, government or company, without the Chinese government's permission, to develop oil and natural gas in waters under Chinese jurisdiction," China Daily reports.
But the Philippines maintains that all of the 15 areas are within Philippine territory.
Philippines Defense Secretary Voltaire Gazmin on Thursday dismissed China's denouncement, saying: "Now, if they get angry, we cannot control their emotions. But then, we still stick to the fact that these [areas] are within our territory. It is ours. Like our president said, 'What is ours is ours.' That's very definite," the Philippine Daily Inquirer reported.
Gazmin said that foreign oil companies that accept the Philippines' invitation to invest in the oil blocks could be assured their operations would be secure, stressing that "investors would not come here if they weren't assured of their safety. We are doing all that we can in order to protect what's ours."
So far, 38 companies have signed up as possible bidders for the oil and gas sites, including Shell Philippines Exploration B.V., Total E&P Activities Petrolieres, Esso Exploration International Ltd. and Spain's Repsol Exploracion S.A.
An editorial published Thursday in China Daily newspaper said the Philippines has chosen "to be a troublemaker."
By inviting major foreign oil companies to invest in exploration of 15 offshore oil and gas areas in the South China Sea, the editorial stated, "the Philippines should assume direct responsibility for the fresh flare-up of the South China Sea issue."
"The Philippines should bear in mind that a number of the 15 areas are under Chinese maritime jurisdiction and it does not have the right to invite foreign enterprises to bid for service contracts there," the editorial said.
China has indisputable sovereignty over the Nansha Islands and adjacent waters and it is unlawful for any country or company to explore oil and gas in areas under Chinese jurisdiction without the permission of the Chinese government," it continued.
Two of the 15 areas -- designated as areas 3 and 4 -- are near the offshore area called Reed Bank, a point of contention last year when two Chinese ships were reported as intimidating a survey vessel.
The South China Sea has proven oil reserves of around 7.7 billion barrels, with estimates reaching to 28 billion barrels.