The strongly worded statement came in response to a news report published Wednesday
saying China has nearly finished building almost two dozen structures on Subi, Mischief and Fiery Cross reefs -- part of the Spratly Islands chain
According to Reuters, US officials said
the structures "appear designed to house long-range surface-to-air missiles," and that building concrete structures on the chain -- where China already has built military-length airstrips
-- "could be considered a military escalation."
At a press conference Wednesday, Chinese Foreign Ministry spokesman Geng Shuang denied any wrongdoing, saying his country strove to preserve "peace and stability" in the region.
He added that China was operating within its territorial rights.
"I want to reiterate that China building facilities, including deploying necessary and appropriate national defense installations in its own territory, is exercising our sovereign right recognized by international law," Geng said.
"We hope other countries respect our efforts and do more to help preserve peace and stability in the region."
At a retreat Tuesday on the Philippine island on Boracay, the Association of Southeast Asian Nations
ministers stressed that demilitarization was a key component of relations between the regional group and China.
"The ASEAN ministers have been unanimous in their expression of concern about what they see as the militarization of the region," Philippine Foreign Secretary Perfecto Yasay told reporters, using the acronym for the group of Southeast Asian countries.
"In so far as certain reclamation of certain features built on the South China Sea that had been completed, they (ASEAN ministers) have noticed, very unsettlingly, that China has installed weapons systems in these facilities that they have established."
Vietnam, Malaysia, the Philippines and Taiwan have also reclaimed land in the South China Sea, but their land grab -- the US says about 100 acres over 45 years -- is dwarfed by China's massive, recent buildup.
The move comes amid growing tensions between China and the United States as President Donald Trump has shown himself more willing to take a confrontational stance with Beijing than his predecessor.
On Saturday, the United States deployed the aircraft carrier USS Carl Vinson
to the disputed waters of the South China Sea as part of maritime "routine operations."
In a news conference last week, China's Foreign Ministry said it heard about the planned deployment of the Vinson days before it happened and warned Washington against challenging its sovereignty.
"China respects and upholds the freedom of navigation and overflight in the South China Sea, which countries enjoy under international law, but firmly opposes any country's attempt to undermine China's sovereignty and security in the name of the freedom of navigation and overflight," the Chinese Foreign Ministry spokesman said at the time.
During his Senate confirmation hearing last month, US Secretary of State Rex Tillerson said China should be blocked from accessing the artificial islands it's built,
setting the stage for a potential showdown.
Dotted with small islands, reefs and shoals, the South China Sea is a crucial shipping route and home to a messy territorial dispute that pits multiple countries against one another.
Tensions in the disputed waters have ratcheted up since 2014 as China has turned sandbars into islands, equipping them with airfields, ports and weapons systems and warned US warships and aircraft to stay away from them.