ISLAMABAD, Pakistan — When President Trump started the new year by suspending billions of dollars of security aid to Pakistan, one theory was that it would scare the Pakistani military into cooperating better with its American allies.

The reality was that Pakistan already had a replacement sponsor lined up.

Just two weeks later, the Pakistani Air Force and Chinese officials were putting the final touches on a secret proposal to expand Pakistan’s building of Chinese military jets, weaponry and other hardware. The confidential plan, reviewed by The New York Times, would also deepen the cooperation between China and Pakistan in space, a frontier the Pentagon recently said Beijing was trying to militarize after decades of playing catch-up.

All those military projects were designated as part of China’s Belt and Road Initiative, a $1 trillion chain of infrastructure development programs stretching across some 70 countries, built and financed by Beijing.

Chinese officials have repeatedly said the Belt and Road is purely an economic project with peaceful intent. But with its plan for Pakistan, China is for the first time explicitly tying a Belt and Road proposal to its military ambitions — and confirming the concerns of a host of nations who suspect the infrastructure initiative is really about helping China project armed might.