China has reclaimed land to extend a reef in the Spratly Islands , in the disputed South China Sea , satellite images show. Photographs taken by American space technology company Maxar showed that Subi Reef – which is also claimed by the Philippines and Vietnam – had new land added to it that had not been visible in a satellite photo taken on February 20. The new rectangle of land, about 2.85 hectares (7 acres) in size, had been added to the southern edge of the ring-shaped coral atoll, which encloses a lagoon and has a channel for vessels to enter and leave. A circular pattern in one corner of the land suggested a tower or radome could be built there, according to Maxar. Collin Koh, a research fellow from the S. Rajaratnam School of International Studies in Singapore, said the new construction could be used for many purposes. “It’s located right along the waterfront, notably,” Koh said. “It’s a probable multipurpose site. There could be buildings and an observation or radar tower, but the open-paved ground is multifunctional. “It can allow for large-scale activities and, perhaps more pertinently, helicopter landing, and even a site for mobile weapon systems or sensors.” Military commentator Song Zhongping said that besides installing military systems, building at the reef “can be used to improve the living environment for soldiers stationed there”. South China Sea: the dispute that could start a military conflict The new construction is the latest of the efforts by China, the Philippines and Vietnam to strengthen their overlapping claims in the South China Sea, where each has built up facilities. China has been dredging and building artificial islands in the Spratlys since 2013, with some equipped with radar, runways and surface-to-air missiles. Subi Reef is one of six artificial islands Beijing has claimed and developed in the South China Sea. It is 26km (16 miles) from Thitu Island, known as Pagasa by the Philippines, which has occupied it and built a beaching ramp. Vietnam has installed emplacements for air and coastal defence systems on most of its bases in the Spratlys, with the most significant upgrades being at West Reef and Sin Cowe Island, according to a report last month by the Centre for Strategic and International Studies’ Asia Maritime Transparency Initiative. Beijing said in 2015 that it had halted land reclamation, a claim not widely accepted by the international community. The next year, an international tribunal ruled that Beijing’s claimed ownership of about 90 per cent of the resource-rich South China Sea had no legal basis. Tensions have flared in the Spratlys this month over the continued presence of a reported 200-plus Chinese vessels near the Beijing-controlled Whitsun Reef, amid complaints that China was turning it into another outpost. When the vessels were spotted in January, Chinese company Chang Guang Satellite Technology said they were sheltering from rough seas, but a continued presence near the reef prompted Manila to label them “maritime militia” and Philippine Foreign Affairs Secretary Teodoro Locsin to file a diplomatic protest with Beijing . The Chinese embassy in Manila on Monday dismissed the militia tag and said the vessels were fishing boats taking shelter.