HELSINKI/LONDON (Reuters) -Estonia has accused neighbouring Russia of jamming GPS navigation devices in airspace above the Baltic states, echoing concerns from airlines that say they have been contending with such interference for months.

Estonian Foreign Minister Margus Tsahkna's accusation, for which he provided no proof, followed Finnair's decision to pause flights to Tartu in eastern Estonia for one month due to GPS disturbances. The Kremlin did not immediately respond to requests for comment.

There have been reports of a rise in GPS interference around the world, particularly since last year, raising fears of an increased risk of accidents if planes veer off-course.

WHAT IS GPS JAMMING AND SPOOFING?

GPS, short for Global Positioning System, is a network of satellites and receiving devices used for positioning, navigation and timing on Earth in everything from ships and planes to cars.

GPS is one of the more important navigation tools in aviation, which has replaced expensive ground devices that would transmit radio beams to guide planes towards landing.

However, it is also fairly easy using store-bought tools to block or distort GPS signals and militaries have invested in technology that can do so.

GPS jamming uses a frequency transmitting device to block or interfere with radio communications, usually by broadcasting signals from the ground that are stronger than satellite-based signals.

Spoofing might involve one country's military sending false GPS signals to an enemy plane or drone to hinder its ability to function and is often considered more disruptive and dangerous than jamming.

The problem for commercial aviation comes if that false signal is picked up by a GPS receiver in a passenger plane, potentially confusing the pilot and air traffic control by showing the wrong time or coordinates without warning.

WHERE DOES IT OCCUR?

In December, aviation advisory body OPSGROUP flagged a surge in spoofing affecting private and commercial jets around the Middle East, including Iraq, Iran and Israel, and the Black Sea.

It tends to impact areas close to war zones as the technology is used to send suicide drones off-track.

Baltic countries have reported the issue for years, particularly since the war in Ukraine began in 2022.

Over the past six months, jamming has worsened around the Baltic Sea, Finnair pilot and Finnish Pilots Association Safety and Security Committee chair Lauri Soini said.

Soini said GPS jamming now occurs in an area extending from Poland across the Baltic states to the Swedish and Finnish coasts, also affecting lower altitudes and maritime traffic.

While politicians and German officials have pointed to Russia as the main culprit in the Baltic states, experts say Western militaries, including U.S. and British forces could be using some form of the technology in parts of the world.

WHY IS IT A PROBLEM FOR AIRLINES?

Most modern airliners have a variety of sensors and sources to determine their positioning, in addition to GPS, meaning they can fly if there is interference.

However, according to pilots and industry experts, airlines still rely primarily on GPS. If jamming or spoofing occurs, GPS might have to be switched off and cannot be reset for the remainder of the flight in many cases.

That can cause stress and delays for take-off and landing because certain procedures require GPS to function.

GPS navigation is also the only form of navigation for some private jets.

However, AirBaltic safety manager and flight captain Janis Kristops said the Tartu incident with Finnair was rare. Most major airports have a variety of navigation tools available if GPS isn't working, he said.

And given the diverse nature of jamming and spoofing devices, it's difficult for the airline sector to come up with a sweeping technological solution that can mitigate the risk.

Instead, authorities are looking to train pilots to verify jamming and spoofing sooner.