BEIJING - A 3,000-metre (9,800-foot) airstrip Beijing is building on a reef in disputed waters in the South China Sea, where tensions are mounting with its neighbours, is "nearly complete", a US think-tank said.
A satellite picture taken on Sunday showed that China was paving and marking the runway on Fiery Cross Reef and an apron and taxiway have been added, the Center for Strategic and International Studies (CSIS) said on its website.
Beijing's project to build artificial islands and facilities on various reefs and outcrops in the Spratly islands only became publicly known in recent months but construction has since been rapid, raising tensions with both its neighbours and Washington.
The US has weighed sending warships and surveillance aircraft within 12 nautical miles - the normal territorial zone around natural land - of the new artificial islands.
A lake in the middle of Fiery Cross Reef has been filled in and it has a partially-developed port with nine temporary loading piers, CSIS said.
Personnel could be seen walking around and two helipads, up to 10 satellite communications antennas and one possible radar tower were also visible, it added.
Washington wants Beijing to halt construction and militarization, which "the Chinese show no indication of willingness to do", Bonnie Glaser of CSIS said.
She anticipated a short-term lull in construction as summer is typhoon season in the South China Sea while China's President Xi Jinping is due to visit the US in September and "the Chinese are attaching priority to having a successful summit".
But she expected activity would pick up again later.
The island is now 2.74 square kilometres (1.06 square miles) in size, CSIS said. China has reclaimed land on seven different reefs totalling an estimated 12.8 square kilometres, it added.
At one of the sites, South Johnson Reef, CSIS said Beijing has added a small port with two loading stations, two helipads on the reef and up to three satellite communications antennas.
It also had a "large multi-level military facility" with two possible radar towers being built, along with up to six security and surveillance towers, and four possible weapons installations.
Beijing claims almost the whole of the South China Sea, including areas close to the coasts of other littoral states, locking it into disputes with several neighbours, particularly the Philippines and Vietnam.
It also has a long-running row with Japan over islands in the East China Sea.
Chinese foreign ministry spokeswoman Hua Chunying said Tuesday that some of the land reclamation works in the Spratlys had been "completed recently as scheduled".
"In the next stage, the Chinese side will start the building of facilities to meet relevant functional requirements," she told reporters at a regular briefing.
They were mainly for civilian purposes, she said, but "necessary military defence requirements will also be fulfilled".