China conducted six successful tests of a new high-speed hypersonic glide vehicle, the most recent in November, and also recently tested an anti-satellite missile, the commander of the U.S. Strategic Command said Friday.

Adm. Cecil D. Haney, the commander in charge of nuclear forces, said the tests are part of a worrying military buildup by China, which also includes China’s aggressive activities in the South China Sea.

"China continues to make significant military investments in their nuclear and conventional capabilities, with their stated goal being that of defending Chinese sovereignty," Haney said during a speech to the Center for Strategic and International Studies.

"It recently conducted its sixth successful test of a hypersonic glide vehicle, and as we saw in September last year, is parading missiles clearly displaying their modernization and capability advancements," he added.

The six tests of the hypersonic glide vehicle, regarded by U.S. intelligence agencies as a nuclear delivery system designed to defeat missile defenses, were first reported by the Washington Free Beacon.

Defense officials said the hypersonic glide vehicle tested on Nov. 23, known as DF-ZF, was launched atop a ballistic missile fired from China’s Wuzhai missile test center in central China.

The glider separated from the booster and flew at extremely high speed—between Mach 5 and Mach 10—along the edge of space.

Haney confirmed all six tests were successful, indicating the weapon program is proceeding.

Prior to the November test, the DF-ZF was flight tested Aug. 19.

The earlier tests were carried out on June 7, and on Jan. 9, 2014; Aug. 7, 2014; and Dec. 2, 2014.

Haney described the hypersonic threat as a challenge to U.S. strategic deterrence.

The congressional U.S.-China Economic and Security Review Commission stated in its latest annual report that the hypersonic glide vehicle program is "progressing rapidly" and the weapon could be deployed by 2020.

China also is building a powered version of the high-speed vehicle that could be fielded by 2025.

"The very high speeds of these weapons, combined with their maneuverability and ability to travel at lower, radar-evading altitudes, would make them far less vulnerable than existing missiles to current missile defenses," the commission stated.

In a second speech to another think tank on Friday, Haney also confirmed that China recently conducted a test of an anti-satellite missile.

Defense officials said the Dong Neng-3 exoatmospheric strike vehicle was flight-tested Oct. 30 from China’s Korla Missile Test Complex in western China. The test was also first reported by the Free Beacon, and officials said the missile threatens U.S. satellites.

Chinese Internet posts of pictures from the area showed what appeared to be contrails from the missile test.

A Chinese military official later confirmed the anti-satellite test in a state-run press report.

Zhou Derong, a professor at the People’s Liberation Army Logistics Academy, described the development of anti-satellite weapons as part of China’s national defense.

"It is perfectly legitimate for China to carry out normal missile launch tests," Zhou was quoted as saying. "Besides, even if China were developing anti-satellite weapons, these would be no more than self-defense measures taken to protect its own space resources."

The official criticized the United States for what he said were efforts to oppose and exaggerate anti-satellite tests.

The DN-3 is the third known anti-satellite missile operational or under development by China. Earlier tests involved anti-satellite missiles known as the DN-1 and DN-2. The DN-1 has also been labeled the SC-19.

Rick Fisher, a China military analyst at the International Assessment and Strategy Center, said Adm. Haney has advanced details of China’s nuclear and strategic developments.

"Adm. Haney is the first U.S. official to call attention to China’s pursuit of prompt global strike capabilities, or non nuclear missile strike systems," Fisher said. "The United States has been talking about Prompt Global Strike for nearly 20 years but has not built any such system."

Also, China’s lack of transparency on nuclear forces is undermining Beijing’s often-stated policy of not being the first to use nuclear arms in a conflict.

"China’s development of two and possibly up to two more MIRV-equipped intercontinental missiles could indicate China seeks a nuclear first strike capability," he said.

China also appears to be seeking to "sprint to parity" with the United States in warhead numbers along with growing space warfare capabilities poses "a much greater danger to U.S. strategic forces," Fisher said, and should prompt a build up of U.S. nuclear forces.

Haney said another concern of Strategic Command is China’s re-engineering of its long-range missile to carry multiple nuclear warheads.

U.S. intelligence agencies detected the test of a new DF-41 intercontinental ballistic missile on Dec. 4 with two independently targetable reentry vehicles, or MIRVs.

By contrast, the United States has removed all multiple warheads from its land-based intercontinental ballistic missiles

Haney, in the CSIS speech, said the current strategic environment is "more complex, dynamic, and volatile, perhaps more so than any time in our history."

"The dangers posed by this unpredictable security environment are compounded by the continuing propagation of asymmetric capabilities and methods, the unprecedented proliferation of advanced capacities and technologies, and the increasingly provocative and destabilizing behavior on the part of both current and potential adversaries," he said.

The threats include terrorists in the Middle East, and activities by nation states including Russia, China, and North Korea.

Russia is continuing to modernize both its conventional and strategic forces and is stressing new strategic approaches and destabilizing activities in Syria and Ukraine, while developing space weapons and conducting cyber attacks, Haney said.

North Korea continues to threaten the Korean Peninsula and the Northeast Asia region with strategic advancements, including claims of "miniaturized" nuclear warheads and recent claims of a successful hydrogen bomb test, the four-star admiral said.

Pyongyang also is developing road-mobile and submarine-launched ballistic missile technologies, he added.

To meet the challenges, Haney said U.S. nuclear forces need to be modernized with new missiles, submarines, and bombers.

"Without timely investment, we risk degrading the deterring and the stabilizing effect of a strong and credible nuclear deterrent force," he said.

Haney also warned about the growing threat of space warfare capabilities.

"We need to get our heads around the fact that a future conflict may bleed into space," Haney said.

"Simply put, the threats are real and are evolving faster than we probably ever imagined. Irresponsible acts in space can have damaging consequences for all space-faring and space-dependent nations."

Space attacks pose "a multifaceted space challenge, and potentially threatens national sovereignty and survival," Haney said.

To counter space threats, the Pentagon is working to counter space attacks on satellites with new capabilities, more secure satellites, and smaller, more easily replaceable satellites.

Both Russia and China are working on space weapons, including lasers and other directed energy weapons that can blind satellites.

The debris resulting from China’s destruction of a weather satellite with a missile in 2007 is still posing problems for satellites and manned spacecraft.

North Korea also appears to be building satellites for space weapons.

"We must be able to maintain situational awareness of it all, act where necessary, and as stated in the 2010 Space Policy, preserve the space environment," Haney said.

The Pentagon is spending more than $5.5 billion to prepare space systems for a future conflict, Haney said.

"We must have assured access to space such that we can function through a multi-layered approach, through all phases of conflict," he said.