In a tantalising find, a team of Italian researchers on Wednesday announced they have discovered a large saltwater lake under ice near the south pole on Red Planet - raising a possibility that life may be there on Mars in some form.

The lake under the Martian ice stretches 20 km across, said the team led by Roberto Orosei from the National Institute of Astrophysics in Bologna in a paper detailed in the prestigious journal Science.

The lake is about 1.5 km beneath Mars's surface and is at least one metre deep.

The detection was made using the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on European Space Agency's Mars Express spacecraft.

If confirmed, it would be the first confirmed news of liquid water ever detected on the Red Planet.

"We discovered water on Mars," said Orosei.

In 2015, in the first-ever definitive signs of the presence of liquid water on the Red Planet, NASA's Mars Reconnaissance Orbiter (MRO) captured strong evidence for seasonal flows of liquid salty water on the Martian surface.

In the new discovery, between May 2012 and December 2015, Orosei and colleagues used MARSIS to survey a region called Planum Australe, located in the southern ice cap of Mars.

They obtained 29 sets of radar samplings, mapping out an area exhibiting a very sharp change in its associated radar signal, about 1.5 km below the surface of the ice and extending sideways about 20 km.

The radar profile of this area is similar to that of lakes of liquid water found beneath the Antarctic and Greenland ice sheets on Earth, suggesting that there is a subglacial lake at this location on Mars.

"Although the temperature is expected to be below the freezing point of pure water, Orosei noted that dissolved salts of magnesium, calcium, and sodium -- known to be present in Martian rocks -- could be dissolved in the water to form a brine," said the study.

"Together with the pressure of the overlying ice, this lowers the melting point, allowing the lake to remain liquid, as happens on Earth," the researchers noted.

According to the journal Nature, if further studies confirm the existence of a lake, it could open new avenues for investigating Mars.

"It begins a new line of inquiry that's very exciting," Jim Green, NASA's chief scientist, was quoted as saying.

Nearly 4.5 billion years ago, Mars had six and a half times as much water as it does now and a thicker atmosphere.

But most of this water has disappeared into space and the reason is that Mars no longer has global magnetic fields, like on the Earth.

The magnetic field protects the Earth's atmosphere against degradation from energy-rich particles from the Sun.

Orosei and team wrote: "There is no reason to conclude that the presence of subsurface water on Mars is limited to a single location."