The Pentagon's main research agency has created the fastest-ever land robot, named "Cheetah", which can gallop at a speed of 29 kilometres per hour.
The headless robot looks to be about the size of a small dog and is shown running on a treadmill in pictures and video released by the defence Advanced Research Projects Agency.
"The robot's movements are patterned after those of fast-running animals in nature," DARPA said in a statement.
"The robot increases its stride and running speed by flexing and unflexing its back on each step, much as an actual cheetah does."
Cheetah's dash has set a "new land speed record for legged robots", beating the previous target of 21.1km/h set by a team at the Massachusetts Institute of Technology (MIT) in 1989, the agency added.
Cheetah can move significantly faster than the average human's running pace but it would not be able to keep up with Olympic gold medallist Usain Bolt, the Jamaican sprinter who has clocked nearly 45km/h.
The robot was created by Boston Dynamics in Waltham, Massachusetts, and was funded as part of DARPA's Maximum Mobility and Manipulation (M3) program, which seeks to advance robotic technology.
Such robots could help the US military to speed up missions to dispose of roadside bombs and better navigate other battlefield perils, the secretive agency said, declining an interview request for more information.
"The use of ground robots in military explosive-ordinance disposal missions already saves many lives and prevents thousands of other casualties," the DARPA statement said.
"If the current limitations on mobility and manipulation capabilities of robots can be overcome, robots could much more effectively assist warfighters across a greater range of missions."
The machine is essentially a laboratory animal for now, powered by an off-board hydraulic pump. A boom-like device helps it stay on track in the centre of the treadmill.
But Alfred Rizzi, Boston Dynamics chief robotics scientist, said field tests for a free-running machine are planned for later this year.
"This machine is really a mostly science-driven project to try and understand the limits of how fast we can actually make a legged machine go," he told AFP.
DARPA has previously funded Boston Dynamics to build other roving robots such as the Big Dog, which can travel up to 20.6 kilometers and navigate wet trails and 35-degree slopes carrying up to 154 kilograms.
Another robot design known as LS3 aims to build on the Big Dog by carrying more weight and travelling further, going "anywhere soldiers and marines go on foot," the company said in a release.
The driver-free LS3 will carry up to 181kg of gear and enough fuel to move 32 kilometers in 24 hours, automatically following a designated leader, or using sensing and GPS equipment to travel on its own.
The LS3, funded by DARPA and the US Marines, is scheduled to make its first public debut later this year.
Despite making major advances in the past five years, the field of battlefield robotics is a long way from manufacturing killing machines to replace soldiers, according to George Pullen, a professor at George Mason University and former DARPA program director.
"There is a general unwillingness to turn lethality over completely to machine intelligence," said Pullen, who is director of the Centre for Excellence in Command, Control, Communications, Computing and Intelligence.
"Trusting an automated system to make life and death decisions is not something that comes naturally to the war fighter.
"It is inevitable that things will progress in that direction but for right now they like to see humans in the loop."
For now, such systems are mainly designed to move things around or carry weapons and cargo, he said.