China has spent years building military outposts on a group of contested islands in the South China Sea — a project that has left the country at odds with many of its neighbors and the United States.

First, there was the dredging, in which ships sucked sediment from the seabed and pumped it atop formerly undeveloped reefs. Then came the buildings — once said to be for civilian purposes but which analysts now say are small military installations — followed quickly by international uproar.

But the building continued. Now, some of the islands that are part of the group known as the Spratlys, where China began large-scale development in 2013, have been transformed from barren reefs into military outposts, as seen for the first time in great detail in a series of new photos.

The images, which were obtained by The Philippine Daily Inquirer from an unnamed source, offer the clearest views yet of the scale of construction and the nature of the military development.