WASHINGTON (REUTERS) - Newly published satellite images show that China is quickly reclaiming land around a submerged reef within an area the Philippines regards as its exclusive economic zone, with several dredgers in operation and seawalls built.
The work on Mischief Reef is China's most recent reclamation in the disputed Spratly archipelago of the South China Sea.
Reclamation is well advanced on six other reefs in the Spratlys, Reuters reported in February, activities that have alarmed other claimants and drawn criticism from Washington.
A March 16 image published by the Washington-based Center for Strategic and International Studies (CSIS) shows what it said were a chain of small artificial land formations as well as new structures, fortified seawalls and construction equipment along Mischief Reef.
Several dredgers are also present while the entrance to the reef had been expanded, the CSIS Asia Maritime Transparency Initiative said on its website.
An image from February 1 showed a Chinese amphibious transport naval vessel about several hundred metres from the reef's entrance. CSIS said such a ship was capable of holding up to 800 troops and as many as 20 amphibious armoured vehicles.
Surveillance photos taken of Mischief Reef in October and seen by Reuters showed no reclamation work.
In an interview with Japan's Yomiuri newspaper published on Wednesday, US Secretary of Defense Ash Carter expressed concern about China's reclamation in the Spratlys.
"We are especially concerned at the prospect of militarisation of these outposts," said Carter, who is in Tokyo on his first visit to Asia as defense chief. Beijing rejects criticism of its activities around the reefs, saying the work falls "within the scope of China's sovereignty".
While the new islands will not overturn US military superiority in the region, Chinese workers are building ports and fuel storage depots as well as possibly two airstrips that experts have said would allow Beijing to project power deep into the maritime heart of Southeast Asia.
The Philippines first said in February that Chinese dredgers had started work at Mischief Reef, 216 km (135 miles) west of the Philippine island of Palawan.
China claims the entire South China Sea. Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims on a waterway where US$5 trillion (S$6.78 trillion) in ship-borne trade passes annually.
China occupied Mischief Reef in 1995. The October photos showed two structures, including a three-storey building sitting on an atoll equipped with wind turbines and solar panels.