China recently built military weapons on contested islands in the South China Sea along busy international trade routes. Video provided by Newsy Newslook

China's military has installed anti-aircraft guns and other weapons on man-made islands in the South China Sea, according to a U.S. think tank's analysis of satellite imagery published late Wednesday.

The Center for Strategic and International Studies' report said China has built "significant point-defense capabilities" on all seven of its outposts in the Spratly Islands archipelago, a key trade channel where Taiwan, Vietnam, the Philippines and others claim territory.

The claim comes as President-elect Donald Trump has accused Beijing of constructing a "massive military complex" in the South China Sea, made aggressive comments about China's trade policy and questioned U.S. protocol and policy over China's rival Taiwan.

Washington-headquartered CSIS based its conclusions on comparisons it made of satellite images taken in the area in June and July with additional ones taken in November. Previous studies by CSIS and others have concluded that China has built airstrips, barracks, radar stations and other infrastructure on the islands.

They "show that Beijing is serious about defense of its artificial islands in case of an armed contingency in the South China Sea,” the CSIS experts wrote in the report. "Among other things, they would be the last line of defense against cruise missiles launched by the United States or others against these soon-to-be-operational air bases," the report said.

China’s defense ministry did not respond to a request for comment. China has previously said that the developments are for civilian navigation while also asserting its right to use them for defense if necessary. President Xi Jinping said last year that "China does not intend to pursue militarization" of the area.

The U.S. has said China's claim to the islands threaten international freedom of navigation law. It said military drills it held in the area are not aimed at China but represent support for regional allies. An international court in The Hague ruled there was no legal basis to China’s claims. Beijing criticized the verdict.

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