A US think tank says Vietnam has rapidly expanded its outposts in the South China Sea, where the country has territorial disputes with China and others.
The Center for Strategic and International Studies released its analysis of satellite imagery and other data.
The center says Vietnam created 2.8 square kilometers of land across 10 features in the Spratly Islands in the six months through May.
It also says the country's overall dredging and landfill has reached 6.5 square kilometers, equivalent to about 40 percent of the areas China has created with its own reclamation work.
The center adds that facilities such as temporary helipads and ports have appeared on Vietnam's outposts.
The CSIS indicates that Vietnam could occupy outposts with a total land area approaching that of China.
CSIS researcher Harrison Pretat says that "with Vietnam's expanded facilities, it too may begin to regularly operate larger numbers of ships in disputed waters."
He says doing so "could lead to more friction with Chinese vessels in the coming years."
Beijing claims sovereignty for almost all of the South China Sea. The country has been carrying out reclamation projects in the Spratly Islands to turn the Mischief and Subi reefs into military outposts.
Vietnam, Malaysia, the Philippines and Taiwan are also building ports and runways on the reefs they control.