WASHINGTON - Recent satellite photographs show China appears to have built reinforced aircraft hangars on its holdings in the Spratly Islands in the disputed South China Sea, the New York Times reported on Monday.

There were no military aircraft seen at the time the photos were taken in late July but the hangars have room for any fighter jet in the Chinese air force, the Times said, citing an analysis of the photos by the Washington-based Center for Strategic and International Studies (CSIS) think tank.

The hangars were constructed on Fiery Cross, Subi and Mischief Reefs, part of the Spratly Islands. China claims most of the South China Sea, through which $5 trillion in ship-borne trade passes every year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei have overlapping claims.

The images have emerged about a month after an international court in The Hague ruled against China's sweeping claims in the resource-rich region, a ruling emphatically rejected by Beijing.

The United States has urged China and other claimants not to militarize their holdings in the South China Sea. China has repeatedly denied doing so, saying the facilities were for civilian and self-defence uses, and in turn criticized U.S. patrols and exercises for ramping up tensions in the region.

The hangars all show signs of structural strengthening, CSIS said.

"They are far thicker than you would build for any civilian purpose," Gregory Poling, director of CSIS's Asia Maritime Transparency Initiative, told the Times. "They're reinforced to take a strike."