AFP/California

US defence secretary Ashton Carter on Saturday warned that land reclamation efforts and a military buildup in the South China Sea could lead to conflict between nations in the region.
Speaking at a defence forum at the Ronald Reagan Presidential Library in California, the Pentagon chief also said America was adapting its military posture to counter increased Russian “aggression”.
Appearing on the final leg of an eight-day trip that included meetings with defence ministers from several nations in the Asia-Pacific region, Carter said his concerns about the frantic pace of land reclamation in the South China Sea were broadly shared.
“The United States joins virtually everyone else in the region in being deeply concerned about the pace and scope of land reclamation in the South China Sea,” Carter told an audience of senior defence figures.
Carter added he was worried about “the prospect of further militarisation, as well as the potential for these activities to increase the risk of miscalculation or conflict among claimant states”.
The Reagan National Defense Forum is an annual event that sees dozens of America’s top defence figures -- including politicians from both political parties -- discuss America’s defence policies.
Carter used his platform to take a swipe at recent Russian military moves.
“At sea, in the air, in space and in cyberspace, Russian actors have engaged in challenging activities,” he said.
“And, most disturbing, Moscow’s nuclear saber-rattling raises questions about Russian leaders’ commitment to strategic stability, their respect for norms against the use of nuclear weapons and whether they respect the profound caution nuclear-age leaders showed with regard to the brandishing of nuclear weapons.”
In an echo of some of Reagan’s own attempts to use technology to counter a Soviet nuclear threat, Carter talked up some of America’s new high-tech weaponry, including an electromagnetic railgun that can fire projectiles at an astonishing 7,250kph.
The defence chief hinted at additional new weapons that would be “surprising ones I really can’t describe here”.
Additionally, “we’re updating and advancing our operational plans for deterrence and defence given Russia’s changed behaviour”, Carter said.
Russia annexed Crimea in 2014 and has been supporting a pro-Moscow separatist conflict in eastern Ukraine.
Carter’s trip was dominated by questions over China’s continued land reclamation efforts and military buildup in the South China Sea.
On Thursday, he flew out to the USS Theodore Roosevelt aircraft carrier as it was sailing in the South China Sea.
The enormous supercarrier was accompanied by the guided missile destroyer the USS Lassen, which last month sailed past a series of islets in Subi Reef in the Spratly Island chain.
There, China is using dredgers to turn reefs and low-lying features into larger land masses for runways and other military uses to bolster its claims of sovereignty in the region.
The Lassen conducted a “freedom of navigation operation” as a way to rebuff China’s those claims.
“We’ve done them before, all over the world. And we will do them again,” Carter said of the sail-by.
Carter said he chose to talk about Russia at the Reagan library as the Cold War was a defining theme of the US leader’s presidency.
Still, he also made some conciliatory gestures to both China and Russia, suggesting there potentially was room for both countries to be part of broader international security structure.
“We do not seek a cold, let alone a hot war with Russia. We do not seek to make Russia an enemy,” he said.
The US navy deliberately avoided military drills or other  actions that could have further inflamed tensions with Beijing during a patrol last week near islands China has built in the South China Sea, US officials said.
“We wanted to assert our rights under international law, but not to the point where we were poking the Chinese in the eye, or where it would unnecessarily escalate the situation,” said a US official, speaking on condition of anonymity.
The official said the destroyer USS Lassen turned off its fire control radars while transiting within 12 nautical miles of Subi Reef and avoided any military operations during that time, including helicopter launches or other drills.
Numerous experts said this cautious approach could in fact reinforce China’s claim to sovereignty over the artificial islands in the Spratly Islands archipelago.
But the official disputed that assertion.
“It was a freedom-of-navigation operation that was not meant to inflame the situation, which is why they did the transit the way they did,” the US official said.
The Lassen’s commanding officer, commander Robert C Francis Jr, told reporters on Thursday that his ship went within six to seven nautical miles of the artificial island.
He said the radar was operating normally at the time for “situational awareness”, and acknowledged the US Navy did not fly helicopters. He described it as both a freedom-of-navigation and a “transit” operation.
China reacted angrily to the patrol, which followed months of US preparation, despite its lack of military drills.
But analysts said that if the Lassen failed to take such actions or even to loiter or collect intelligence within the zone, the operation would have resembled what is known as “innocent passage,” and could have reinforced rather than challenged China’s claim to a territorial limit around the reef.
“Innocent passage” occurs when one country’s ship quickly transits another’s territorial waters - and can only take place in waters belonging to another country.