China has almost finished building around two dozen structures on artificial islands in the South China Sea. The buildings will reportedly house long range surface-to-air missiles, two US officials have said.

"It is not like the Chinese to build anything in the South China Sea just to build it, and these structures resemble others that house SAM batteries, so the logical conclusion is that's what they are for," a US intelligence official told Reuters.

He added that the structures did not pose any military threat to US forces in the region.

"The logical response would also be political – something that should not lead to military escalation in a vital strategic area," he said in an exclusive report by Reuters.

A second official said that the structures appeared to be 20m long and 10m high.

A spokesperson for the Pentagon said that the US is committed to "non-militarization in the South China Sea" and asked claimants involved to act according to international law.

The Chinese embassy in Washington did not respond to Reuters' request for comment.

China lays claim to all of South China Sea, which sees a third of world's maritime traffic. Other countries such as Vietnam, Brunei, the Philippines, Taiwan and Malaysia have also claimed parts of the sea.

In recent days, US officials also said that building concrete structures with retractable roofs on Fiery Cross, Subi and Mischief reefs, which are part of Spratly islands, could be viewed as military escalation.

The Philippines on Tuesday, (21 February) said that South Asian countries viewed the weapons instalation in South China Sea as "very unsettling" and have asked for a dialogue in the wake of recent developments.

South China Sea
Chinese dredging vessels are purportedly seen in the waters around Mischief Reef in the disputed Spratly Islands in the South China Sea in this still image from video taken by a P-8A Poseidon surveillance aircraft provided by the United States NavyU.S. Navy/Handout via Reuters/File Photo