Images show Vietnam's South China Sea land reclamation

Newly released images show Vietnam has carried out significant land reclamation at two sites in the disputed South China Sea, though the scale and pace is dwarfed by China’s own land reclamation projects, a U.S. research institute said Friday.

The photographs show the expansion of the land area and the addition of buildings at Vietnamese-controlled Sand Cay and West London Reef in the Spratly archipelago.

Mira Rapp-Hooper, director the Asia Maritime Transparency Initiative at the Center for Strategic and International Studies, said there were military installations located on the reclaimed land. Hanoi launched its expansion project before China began a flurry of land reclamation projects last year.

The photographs were taken by satellite imagery firm DigitalGlobe between 2010 and April 30 this year.

"On one site, [Hanoi] has constructed a significant new area that was formerly under water and at another it has used land reclamation to add acreage to an existing island," Rapp-Hooper said.

In response, China condemned Vietnam's actions, and said its own land reclamation work in the region was done out of obligations to the international community to improve navigation safety and contribute to science and research, including building observation platforms to monitor sea levels. 

China claims more than 90 percent of the potentially energy-rich South China Sea, displaying its reach on official maps with a so-called nine-dash line that stretches deep into the maritime heart of Southeast Asia — much to the chagrin the Philippines, Malaysia, Brunei, Taiwan and Vietnam.

Vietnam's government did not immediately respond to a request for comment, but it routinely says it has sufficient legal and historical evidence to support its claims in the Spratlys.

Just last month, Hanoi and Beijing pledged to bolster diplomatic ties and look for a solution in the South China Sea that both countries could accept.

On April 7, Chinese state news agency Xinhua reported that Beijing and Hanoi had a "candid" exchange and pledged to overcome their long-standing maritime spat to improve diplomatic ties. 

But in response to the newly released images of Vietnam's projects, Chinese Foreign Ministry spokeswoman Hua Chunying said that the reclamations were occurring on what she called illegally occupied Chinese islands.

"We demand that the relevant countries stop all their activities which infringe upon China's sovereignty and rights," she told a daily news briefing.

Hua added that China's building work was partly to better fulfill its international obligations, including as part of a deal agreed at a UNESCO meeting in Paris in 1987. There, she said, China was entrusted to build five out of 200 sea level observation platforms, including on the Spratlys.

"The scale of China's construction should be commensurate with its responsibilities and obligations as a major country," Hua added.

The speed of recent Chinese reclamation work has alarmed its neighbors and the United States, which sees it as a potential threat to the status quo in a region through which $5 trillion of sea-borne trade passes each year.

New Vietnamese military facilities at Sand Cay appeared to include defensive positions and gun emplacements. What appeared to be new buildings on West London Reef could also have military applications, Rapp-Hooper said.

"Strictly speaking, these photos show that China is right," Rapp-Hooper said, "but we can safely say that the scope and scale of what China has undertaken is totally unprecedented and dwarfs Vietnam's activities many times over."

She said the images show that Vietnam had reclaimed about 699,654 square feet of land at West London Reef and 226,042 square feet at Sand Cay.

China, by comparison, had reclaimed 9.6 million square feet of land at a single South China Sea reef, Fiery Cross. Rapp-Hooper said satellite images show that since about March 2014, China had conducted reclamation work at seven sites in the Spratlys. Beijing is constructing a military-sized airstrip on one artificial island and possibly a second on another, she said. She added that Vietnam already had an airstrip on the Spratlys.

The U.S. State Department and Pentagon had no immediate comment on the latest images. U.S. President Barack Obama last month accused China of "flexing its muscles" to advance its maritime claims.

Al Jazeera and wire services