Tensions over China's island-building in the South China Sea may have eased in the past year, but Beijing has kept busy.
New satellite imagery shows China has built infrastructure covering 72 acres (28 hectares) in the Spratly and Paracel islands during 2017 to equip its larger outposts to be air and naval bases.
The Washington-based Asia Maritime Transparency Initiative closely tracks developments in the South China Sea, where China and several Asian governments have conflicting territorial claims. It said on Thursday there has been construction of hangars, underground storage, missile shelters, radar arrays and other facilities.
The activity comes as China joins what are likely to be protracted negotiations with Southeast Asian nations on a "code of conduct" for South China Sea. Tensions with the US on the issue have also eased, despite Washington's criticism of Beijing's conduct.
The construction is the follow-up phase to a campaign of land reclamation that was completed by early 2016 in the Spratlys, an island chain where Malaysia, Taiwan, the Philippines, Vietnam and Brunei also have claims. According to the Pentagon, China has added more than 3,200 acres (1,248 hectares) of land to the seven land features it occupies in the area.
China also seems to have halted smaller-scale operations to expand islands in the Paracels that lie farther north, the initiative said.
The US and others have accused Beijing of further militarizing the region and altering geography to bolster its sweeping claims across the South China Sea. China says the man-made islands in the Spratlys, which are equipped with airstrips and military installations, are mainly for civilian purposes and to boost safety for fishing and maritime trade.
Greg Poling, the initiative's director, said China had seized a diplomatic opening after the election of Philippine President Rodrigo Duterte, who adopted a conciliatory stance toward Beijing over their territorial dispute. It's also been less of a focus for President Donald Trump's administration, preoccupied by North Korea's nuclear threat 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. They are continuing all the construction they want," Poling said.
The most construction has been on Fiery Cross Reef in the Spratlys, including hangars alongside its 10,000-foot (3,000-meter) airstrip, underground structures likely intended to house munitions or other materiel, hardened shelters for missile platforms, and communication and radar facilities, the initiative said.
It also noted that China has deployed new military aircraft at Woody Island in the Paracels. At the end of October, the Chinese military released images of J-11B fighter planes there for drills. In mid-November, Y-8 transport aircraft were spotted on the same island that may be capable of electronic intelligence gathering.
Marine Lt. Col. Christopher Logan, a Pentagon spokesman, said Thursday that he could not comment in detail on US assessments of the region but that "further militarization of outposts will only serve to raise tensions and create greater distrust among claimants."
The United States does not claim territory in the South China Sea but has declared it has a national interest in ensuring that the territorial disputes there are resolved peacefully in accordance with international law and that freedom of navigation and overflight are guaranteed. China has opposed what it calls US meddling in an Asian dispute.