As China rapidly builds new artificial islands in the South China Sea to expand its territorial claims there, Washington is adamantly refusing to recognise those claims.

On Saturday, US Defence Secretary Ash Carter called on Beijing to stop amid fresh tensions, CNN reported.

Last week, a US surveillance plane swooped over such artificial islands, triggering eight warnings from the Chinese navy to back off. US officials were concerned about China’s militarisation of some of the islands and were trying to create public awareness about it.

Carter reiterated the issue of land reclamation at a conference of diplomats and international experts in Singapore.

“The US is deeply concerned about the pace and scope of land reclamation in the South China Sea, the prospect of further militarisation as well as the potential for these activities to increase the risk of miscalculation or conflict among claimant states,” Carter said in a speech before the diplomats.

There is tension over the South China Sea among China and neighbouring countries such as Vietnam and the Philippines, which have argued about existing territorial claims and mineral rights.

Some of these nations have also built a few artificial islands as well.

But of the governments participating in land reclamation, Carter singled out Beijing for particular criticism.

“One country has gone much further and much faster than any other, and that’s China. China has reclaimed over 2,000 acres, more than all other claimants combined and more than in the entire history of the region. And China did so in only the last 18 months.”

Although he expressed concern over possible conflicts, Carter said solutions are limited. “We all know there’s no military solution to the South China Sea disputes,” he said and called for renewed diplomacy.