Story highlights Pentagon's annual report to Congress raises concerns

China has developed thousands of acres on disputed islands

(CNN) Satellite photos show China has been rapidly building military outposts on disputed islands in the South China Sea, significantly boosting its presence in the already tense region, according to a Pentagon report released Friday.

"China continues to invest in military programs and weapons designed to improve power projection, anti-access area denial and operations in emerging domains such as cyberspace, space and the electromagnetic spectrum," said Abraham Denmark, deputy assistant secretary of defense for East Asia.

The report to Congress reveals that China has added over 3,200 acres to the seven sites it occupies in the South China Sea during the last two years.

On these artificial island sites, China has excavated deep channels to improve access to its outposts, created artificial harbors, dredged natural harbors and constructed new berthing areas to allow access for larger ships, according to the Pentagon's annual China Military Power report.

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