NEAR SHAYMAK, Tajikistan — Two miles above sea level in the inhospitable highlands of Central Asia, there’s a new power watching over an old passage into Afghanistan: China.
For at least three years, Chinese troops have quietly monitored this choke point in Tajikistan just beyond China’s western frontier, according to interviews, analysis of satellite images and photographs, and firsthand observations by a Washington Post journalist.
While veiled in secrecy, the outpost of about two dozen buildings and lookout towers illustrates how the footprint of Chinese power has been expanding alongside the country’s swelling economic reach.
Tajikistan — awash in Chinese investment — joins the list of Chinese military sites that includes Djibouti in the strategic Horn of Africa and man-made islands in the South China Sea, in the heart of Southeast Asia.
Meanwhile, Chinese President Xi Jinping’s economic ambitions over the past seven years have brought a wave of major investment projects, from the resource-rich Caspian Sea to Cambodia’s coastline.
The modest facility in Tajikistan — which offers a springboard into Afghanistan’s Wakhan Corridor a few miles away — has not been publicly acknowledged by any government.
But its presence is rich in significance and symbolism.
At a moment when the United States might consider a pact that would pull American troops out of Afghanistan, China appears to be tiptoeing into a volatile region critical to its security and its continental ambitions.
Already, the retreat of old powers and arrival of the new are on display in Tajikistan, a tiny, impoverished country that served as a gateway into Afghanistan for US units in the early phases of the 2001 invasion.
During a recent trip along the Tajikistan-Afghanistan border, The Post saw one of the military compounds and encountered a group of uniformed Chinese troops shopping in a Tajik town, the nearest market to their base. They bore the collar insignia of a unit from Xinjiang, the Chinese territory where authorities have detained an estimated 1 million Uighurs, a mostly Muslim ethnic minority.
Details about China’s activities at the facilities, some of which bear the Chinese and Tajik emblems, are not made public. Also unclear are the arrangements over their funding, construction and ownership. Satellite imagery shows what appear to be two clusters of buildings, barracks and training grounds, about 10 miles apart near the mouth of the Wakhan Corridor, a narrow strip of territory in northeastern Afghanistan.
China’s Foreign Ministry declined to comment and directed questions to the Defense Ministry, which did not respond to requests for comment.
Tajikistan’s Foreign Ministry said there are ‘‘no People’s Republic of China military bases on the territory of the Republic of Tajikistan,’’ nor ‘‘any talks whatsoever’’ to establish one.
US officials say they are aware of the Chinese deployment but do not have a clear understanding of its operations. They say they do not object to the Chinese presence because the United States also believes that a porous Afghan-Tajik border could pose a security risk.
China’s encroachment into Afghanistan is ‘‘fascinating but not surprising — and should be welcomed by Washington,’’ said Ely Ratner, executive vice president at the Center for a New American Security, who was a deputy national security adviser to Vice President Joe Biden.
The projects reflect Tajikistan’s strategic position in China’s Belt and Road Initiative, an ambitious infrastructure investment plan to pull the Eurasian land mass into its economic embrace.
China, through a single state bank, held more than half of Tajikistan’s external debt as of 2016, up from none in 2006, according to 2017 Tajik Finance Ministry data.
Susan Elliott, former US ambassador to Tajikistan, said China’s generous aid and funding should be applauded but viewed with skepticism. In the past year, a handful of countries that have taken Chinese investments have reconsidered initiative deals amid allegations of corruption and low feasibility.