Bangkok: China has been busy building military infrastructure in the South China Sea while the United States and its key allies, including Australia, have been distracted by the North Korean nuclear crisis.
New satellite images show China's military has built high frequency radar and other facilities on islands it occupies, even as Beijing was signalling its willingness to pursue protracted negotiations on a "code of conduct" with other claimants to the flashpoint waters.
The Washington-based Asia Maritime Transparency Initiative, which closely tracks developments in the South China Sea, said China has been constructing hangers, underground storage bunkers, missile shelters, radar arrays and domes and other facilities that cover 28 hectares.
The revelation comes as China's naval chief Shen Jinlong told his Australian counterpart, Vice Admiral Tim Barrett that Canberra's actions in the South China Sea run counter to the general trend of peace and stability in one of the world's most important shipping lanes.
"This does not accord with the consensus reached by the leaders of the two countries nor the atmosphere of the forward steps in cooperation in all areas between the two countries," Jinlong said during a meeting in Beijing.
Australia has flown surveillance flights over the South China Sea and supports US patrols near the Chinese-held islands to assert what Washington sees as right to free passage in international waters.
Earlier this week, before the release of the images, US Secretary of State Rex Tillerson called for a "freeze" in China's island building and said it was unacceptable to continue their militarisation.
Pentagon spokesman Christopher Logan said he could not comment in detail on the images but that "further militarisation of outposts will only serve to raise tensions and create greater distrust among claimants."
The US has conducted multiple patrols near the Chinese-held islands this year to assert what it sees as right to free passage in international waters.
But analysts say the Trump administration has yet to implement a coherent strategy on the dispute after initially suggesting the US might deny Chinese access to the islands.
China's latest construction follows land reclamation that was completed in early 2016 in part of the sea known as the Spratlys, an island chain where Malaysia, Taiwan, the Philippines, Vietnam and Brunei have completing claims.
The US claims China has built-up 1248 hectares of land on seven islands over nearly a decade but at accelerated speed since 2014.
Most of the construction has been on Fiery Cross Reef where there is a 3000-metre airstrip, underground structures likely intended to house munitions and other military infrastructure.
At the end of October, China released images of jet fighter planes and military transport planes at Woody Island in the Paracels, another part of the disputed waters.
The island is China's military and administrative headquarters.
The latest construction includes two large radar towers on Triton Island in the Paracels that has been the scene of tense stand-offs between Chinese and Vietnamese ships in recent months.
Greg Poling, director of the Asia Maritime Transparency Initiative, said China seized a diplomatic opening after the election last year of Philippine president Rodrigo Duterte, who adopted a conciliatory stance toward Beijing over the territorial dispute, and as the US was preoccupied with North Korea and trade disputes with China.
"It's gotten off the front pages but we shouldn't confuse that with a softening in China's pursuit of its goals," Mr Poling said.
"They are continuing all the construction they want," he said.
The dispute has caused deep anxiety within Australia's defence and diplomatic circles.
Australia opposes any build-up of the islands and their militarisation and has publicly called for China to pursue a "rules based order" and "peaceful solution" to the disputes.
China lashed Australia over its recent foreign policy White Paper, saying language used on the South China Sea was "irresponsible."
"Australia is not a party to the South China Sea issue," Chinese Foreign Ministry spokesman Lu Kang said at the time.
The South China Sea is one of the world's most important shipping lanes.
More than half of Australia's coal, iron ore and LNG exports pass through the waters.
- with agencies