China says the work is needed to safeguard its sovereignty.
China claims almost the whole of the South China Sea,
resulting in overlapping claims with several other Asian nations including
Vietnam and the Philippines.
They say China is illegally reclaiming land in contested
areas to create artificial islands with facilities that could potentially be
for military use.
Images have emerged of work in multiple areas in the Spratly
islands, which several nations claim.
'Elbowed aside'
The most recent images, from the Centre for Strategic and
International Studies, showed work on Mischief reef.
The think tank published before-and-after satellite
pictures showing man-made islands with runways and harbours, and Chinese
vessels dredging sand on to the reef.
Asked about the issue during a visit to Jamaica, Mr Obama
said the views of smaller claimant nations had to be considered.
"Where we get concerned with China is where it is not
necessarily abiding by international norms and rules, and is using its sheer
size and muscle to force countries into subordinate positions," he said.
"We think this can be solved diplomatically, but just
because the Philippines or Vietnam are not as large as China doesn't mean that
they can just be elbowed aside."
Hours earlier, China gave one of its most detailed comments
on the issue at a foreign ministry daily press briefing.
Spokeswoman Hua Chunying said (transcript in
Chinese) that China had "indisputable rights" to the Spratly islands,
and that it was only "protecting the country's national sovereignty and
maritime rights".
The construction was to serve troops protecting the area and
civilian activity such as search and rescue operations, scientific research and
commercial fishing, she said.
"The structures... do not affect, nor are they targeted
at, any particular country," she said, adding that China would
"continue to strengthen" its activities in the area.
Rupert Wingfield-Hayes: China's
Island Factory
I stare out at the endless rolling waves. On the horizon the
sky is dark and threatening. Then my eye is caught by something sticking up
above the waves. It looks like an oil or gas-drilling platform. What on earth
is it doing here?
As we get closer, to my right, I am sure I can now see
something pale and sandy beside the platform. "That looks like land!"
I say. It can't be. I look at my GPS.
There is no land marked anywhere near here, only a submerged
reef of the Spratly Island chain. But my eyes are not deceiving me. A few
kilometres away I can now clearly see the outline of an island.
In recent days, several senior US officials have weighed in
on China's land reclamation work, warning it raises regional tensions.
The commander of the US Pacific fleet, Adm Harry Harris,
said in a speech in Australia last week that China was "creating a great
wall of sand with dredges and bulldozers".
He said that work to date had created more than 4 sq km (1.5
sq miles) of artificial land mass.
US Navy Lt Cmdr Wilson VornDick wrote in
an analysis on the CSIS website: "It appears that China's
building projects are part of an expansive territorial grab or to make China's
disputed Nine-Dash Line claim a reality."
The Nine-Dash line is a boundary which China uses to
demarcate its claims in the South China Sea. It is not recognised outside
China.
The row has already led to conflict. When China placed an
oil rig in waters claimed by Vietnam last year, anti-China riots erupted.
The Philippines has filed a complaint with UN's Permanent
Court of Arbitration - but China says it will not engage with the case.
Source: BBC