U.S. Secretary of State John Kerry visited Beijing Saturday to urge China to scale back its reclamation work in the disputed South China Sea territory known as the Spratly Islands in an effort to reduce the increasing tensions among the countries claiming the reefs, but his appeal was strongly rejected by Chinese Foreign Minister Wang Yi.

Speaking at a news conference, Kerry said, "I urged China, through Foreign Minister Wang, to take actions that will join with everybody to help reduce tensions and increase the prospect of a diplomatic solution."

Wang replied that China's actions in ensuring its sovereignty over the territory is "a legitimate right" that is "unshakeable."

"The determination of the Chinese side to safeguard our own sovereignty and territorial integrity is as firm as a rock," he said, according to The New York Times.

Kerry was reportedly in China to discuss the annual White House summit meeting between President Obama and President Xi Jinping, which will happen in June. He also discussed other issues with Wang, including the nuclear program of Iran and U.S. and China military relations.

But one of his major concerns for the visit was to see a visible resolution to the escalating tension in the disputed reefs in the South China Sea, which is being claimed by five other different nations besides China: The Philippines, Vietnam, Malaysia, Taiwan and Brunei.

China's reclamation efforts in the islands and the fast construction of a concrete runway in one of the islands that can be used for military aircraft has alarmed the countries that are staking their claim to the territory, particularly The Philippines, which is a known American treaty ally. The Spratly Islands lie just off the coast of the Philippines but are 1,000 miles away from the southernmost point of China.

According to Kerry, the U.S. is not taking any position on the territorial dispute, but based on international law, a country cannot establish sovereignty over the region by undergoing reclamation projects. He said the U.S. is concerned about the scale of China's rapid work in the Spratly Islands.

He emphasized that "smart diplomacy," not "outposts and military strips," is what is needed at this time, according to Reuters.

Kerry also said that the U.S. is "committed to maintain freedom of navigation" in the area, which is one of the busiest shipping lanes in the world. He added that China's building of artificial islands could have a negative effect not only on China's relationship with its neighboring countries but also with the U.S., according to the South China Morning Post.

However, China remains unflinching in its claim over the reefs and atolls. "It is all right that China and America have diverging ideas on the South China Sea issues. But we shall not have misunderstanding or misjudgment," Wang said.

He also interjected concerns about the U.S. sending military ships and aircraft to see to its goal of imposing freedom of navigation in the area.

According to Reuters, the Chinese foreign minister said, "With regard to construction on the Nansha islands and reefs, this is fully within the scope of China's sovereignty," adding that it is "the people's demand of the government."