"The Pentagon was aware of the launch of the Chinese rocket from the artificial structures in the South China Sea near the Spratly Islands," said Lieutenant Colonel Dave Eastburn.
More tests were expected, NBC said, citing unnamed US officials.
CNN has asked the Chinese authorities to comment on the report.
China has claimed nearly the entire 1
To reinforce its claim, China has created artificial islands in the chain in the southern part of the South and attached China Sea, despite a pledge made by President Xi Jinping during a visit to the White House in 2015, that the islands have no military outposts would become.
"What is really troubling about this act is that it directly contradicts President Xi's statement … that he would not militarize these artificial outposts," Eastburn said Tuesday.
"I will not speak for all the sovereign nations in the region, but I am Certainly that they agree with this (Chinese) behavior. This contradicts his claim to bring peace to the region, and apparently such acts are acts of coercion intended to intimidate other applicants (in the South China Sea), "Eastburn added.
the South China Sea. The US and its allies and partners are strengthening their presence in the region.
In June, one of the US Navy's largest warships, the USS Ronald Reagan aircraft carrier, joined Izumo, one of Japan's largest naval ships, the helicopter destroyer JS, for exercises in the South China Sea.
At the weekend, the US Navy announced that the USS Montgomery coastal battleship would launch a port in Davao, Philippines. It is expected that the shallow draft ship, designed for use near coasts and islands, will be brought to Singapore as part of a plan by the US Navy to ship two ships this year.
Meanwhile, warships from Australia became Canada and France have been in and around the South China Sea for the past 12 months as the US encouraged its allies to support a free and open region in the Indo-Pacific.
The tension in the Spratlys was particularly high last month after a Filipino fishing boat went down after a collision with a Chinese fishing boat on 9 June.
The Filipino fishermen said they were drowned by the Chinese boat and were only rescued hours later by a Vietnamese boat. China claims its ship is threatened by raving Philippine boats.
The incident was enough to send a diplomatic protest to Beijing in Manila, although the government of President Rodrigo Duterte has apparently not been ready to push Beijing forward on this issue.
Ryan Browne of CNN has contributed to this report.