ECS is the area of the continental shelf that is under shallow water.
The area of the United States grew by 386,000 square miles (6.21 lakh square kilometres) last month after the Department of State (DOS) added six regions' submerged offshore areas, called extended continental shelf (ECS), to the total landmass, according to a report in Metro. The ECS is the area of the continental shelf that is under shallow water, beyond 200 nautical miles. The largest ECS area for the US is the Arctic - 350 miles (612 km) to the north and more than 680 miles (1,094 km) in the western region - the outlet further said.
According to USGS, it is an important maritime zone that holds many resources and vital habitats for marine life.
The agency said that America's ECS includes six other regions: The Atlantic east coast, the Pacific west coast, the Bering Sea, the Mariana Islands and two portions of the Gulf of Mexico.
"Like other countries, the United States has rights under international law to conserve and manage the resources and vital habitats on and under its ECS," the State Department said in the announcement.
The land area added to the US territory is nearly twice the size of Spain.
Wilson Centre, a think tank based in Washington, DC, said that ECS extension has major implications for US's efforts to secure its territorial rights in the Arctic region.
"It has long been clear that the United States has major economic interests in undersea territory rich in oil, natural gas, minerals and sea life to which it has sovereign rights under the law of the sea as reflected in the Law of the Sea Convention," the think tank was quoted as saying by Metro.
Wilson Centre also said that the US has the largest exclusive economic zone on the planet, which helps it safeguard its sovereign rights to areas submerged under water.
"It is also an important milestone reflecting US engagement with the law of the sea as reflected in the UN Convention on the Law of the Sea and as an aspect of advancing major US interests in the Arctic and other regions," said the Wilson Centre.
The extension of the ECS is based on the analysis of data collected by National Oceanic and Atmospheric Administration (NOAA) and USGS.