China tried to electronically jam U.S. drone flights over the South China Sea in a bid to thwart spying on disputed island military construction, U.S. officials said.

Global Hawk long-range surveillance drones were targeted by the jamming in at least one incident near the disputed Spratly Islands, where China is building military facilities on Fiery Cross Reef.

Disclosure of the jamming came as a U.S. Navy P-8 surveillance flight on Wednesday was challenged eight times by the Chinese military to leave the same area.

"This is the Chinese navy … This is the Chinese navy … Please go away … to avoid misunderstanding," a radio call in English from an installation on Firey Cross said. The warnings were reported by CNN, which had a reporter on the aircraft.

Later Thursday, the Navy released video revealing that the China’s People’s Liberation Army Navy sent several radio warning messages to the crew of the P-8 ordering the jet to leave the area, and to deviate from its flight path near Fiery Cross Reef.

A Navy officer aboard the militarized Boeing 737 aircraft is quoted on the video saying an airstrip under construction on Fiery Cross Reef is "hundreds of meters" long and was built on the reef in the past several months.

It was the first time operations by the P-8, a new surveillance aircraft that is armed with torpedoes, were disclosed by the Navy.

At the Pentagon, spokesman Col. Steve Warren said the United States does not recognize China’s sovereignty claims over the new islands and said P-8 aircraft and Navy ships have not gone within 12 miles of the islands. "That would be the next step," Warren told reporters. Asked about plans for transiting the close-in areas, Warren said: "We don't have any announcement to make on next steps. We are going to continue our routine flights."

Details of the drone interference are classified. A spokesman for the Hawaii-based Pacific Command and Pacific Air Force declined to comment on the jamming.

On the Chinese challenge of the P-8 flight, Pacific Command spokesman Capt. Chris Sims sought to play down the incident.

"There have been a number of times when these PACOM forces have been queried by [People’s Liberation Army] PLA forces, but we have continued on without altering our planned activities," Sims said.

Regarding South China Sea drone flights, Sims said there were no Chinese aerial intercepts against U.S. unmanned aerial vehicles over the disputed waters that China is claiming as its maritime domain. Sims said he cannot confirm jamming or electronic warfare reports, and would not elaborate in an email.

Pacific Air Forces spokeswoman Rebekah Clark declined to comment on Global Hawk surveillance flights near the Spratlys because of "operational security."

The high-altitude drones are based at Anderson Air Force Base in Guam on a rotational basis. "From Guam, the Global Hawk supports U.S. intelligence, surveillance, and reconnaissance priorities, operational plans, and contingency operations through the Pacific Theater," Clark said.

The RQ-4 Global Hawk is the Air Force’s premier high-altitude, long-range surveillance drone that can fly remotely piloted missions, and missions that are programmed in advance, and can survey 40,000 square miles in a day.

The 47-foot long jet-powered drone has a range of 8,700 miles and can fly up to 60,000 feet in altitude. Its flying time is up to 28 hours.

Last week, David Shear, the assistant defense secretary for Asian and Pacific security affairs, said Global Hawks are deployed in Asia as one element of a buildup of forces near the South China Sea.

"We’re engaged in a long-term effort to bolster our capabilities in the region," Shear told the Senate Foreign Relations Committee. "Just a few examples of the increases in our capabilities in the region include the deployment of Global Hawks and F-35s. Soon we will be adding to the stock of V-22s in Japan as well."

Shear said the Pentagon estimates that China will complete construction of an airfield on Fiery Cross Reef by 2017 or 2018.

A Navy littoral combat ship, the USS Fort Worth, earlier this month sailed near the Spratlys on what was dubbed a freedom of navigation mission.

A Navy press release about ship’s operations stated that the Fort Worth dispatched an unmanned Fire Scout helicopter drone and a manned helicopter during the cruise. However, Darryn James, a Pacific Fleet spokesman, later said the Navy press release was incorrect and that the drone was not launched. He provided no explanation for the error.

Chinese military writings have discussed using electronic means to disrupt drone surveillance.

A February 2013 technical article in the journal Aerospace Electronic Warfare revealed in detail how China’s military planned to detect and to counter Global Hawk surveillance flights, as well as RQ-170 drone operations. Both are radar-evading stealth surveillance drones.

"The American military has an advanced theater control network but it also has its vulnerabilities," the article states.

"We can use network warfare to attack and even control America’s network," the report says. "UAVs and ground stations are normally quite far apart and usually have to depend upon satellite communications. As long as we can disrupt its satellite communications, drones will be unable to carry out missions and will have to return its base."

The report said Global Hawk drones have seven vulnerabilities, including being open to electronic interference. Jamming "will greatly reduce the effectiveness of Global Hawk," the article states.

Rick Fisher, a China military affairs analyst, said China could increase pressure on the United States to halt surveillance flights in Asia by first attacking one of the unmanned aircraft flights.

"Though UAVs like the Global Hawk are rather expensive, they are also regarded as more expendable because they are unmanned," said Fisher, a senior fellow at the International Assessment and Strategy Center.

"But failing to defend these UAVs runs the risk of China viewing them as ‘fair game’ to shoot down whenever they please."

Beijing also might attempt to capture a Global Hawk by causing one to crash in shallow water, or by attempting to snatch one in flight using a manned aircraft.

The United States should balance its unmanned high-altitude surveillance systems with high-altitude piloted aircraft that are better able to conduct evasive maneuvers and use defensive systems, Fisher said.

China has been building up new islands in the area, using special dredging ships that pump sand from underwater. According to U.S. officials, over the past several years, some 2,000 acres of islands have been reclaimed in the South China Sea.

Now China is building military facilities on the reclaimed land that will be used to exercise military control over what China is calling the Nine-Dash Line covering most of the South China Sea that Beijing claims as its maritime domain.

Those claims are disputed by Vietnam, the Philippines, and other states in the region.

"Last year was the time to start freedom of passage challenges as China was just starting to build its new military bases atop the global strategic economic arteries of the South China Sea," Fisher said.

"Waiting until this year means that China will sooner have the tactical advantage of being able to put military forces on its new bases to challenge U.S. sorties into this region," he added. "It is likely that by this fall, the People’s Liberation Army will be able to start placing weapons on these islands—radar plus anti-air and anti-ship missiles first, then PLA Navy J-11B air superiority fighters."

Once the bases are set up, Fisher said the Chinese will use them to keep U.S. forces out of the region.

"China’s island building is a clear attempt to gain a dominant military position in this region," Fisher said.

"In response the U.S. should be cooperating with … the Philippines, offering Philippines multiple squadrons of multirole fighters and offering them hundreds of ATACMS short range ballistic missiles able to blast China’s islands if China should attack Philippine assets."

Fisher said only when U.S. and Philippines forces have the capability to destroy China’s new island bases will there be any chance that Beijing will consider reasonable behavior.