Estonia's Ministry of Defence (MoD) has accused Russia's military of violating the Nato member's airspace for the fourth time in 2016, a claim denied by Moscow. Estonia claims Russian planes regularly approach or intrude into the country's air space.

In a statement Estonia claimed the Russian Antonov An-72 transport aircraft flew close to the northern island of Vaindloo in the Baltic Sea for around 90 seconds at 18.23 local time on Monday evening (5 September). The statement said the Russian pilot ignored Estonia's air traffic control despite its responders being switched on.

There have been regular squabbles between the Nato alliance and Russia in the Baltic region, which is close to the Russian border. Both sides accuse the other of ignoring transponders, though according to Postimees newspaper most Russian planes are fitted with Soviet-era transponders which render Western civilian radar "blind" to them.

This transponder issue could result in a civilian airliner accidentally colliding with a Russian jet, said Postimees. The newspaper quotes an anonymous Russian officer who admitted most Russian jets don't even possess transponders.

Russia's Ministry of Defence spokesman Igor Konashenkov told state news agency Itar-Tass that no Russian planes were in the area at the time of the alleged incident. "Aircraft from Russia's air force regularly carry out flights over the Baltic Sea, however their routes fall strictly within international rules and regulations on using airspace and neutral waters," said Konashenkov, according to Newsweek.

Bulgaria, also a Nato member, says Russia violated its airspace on 10 occasions in July 2016 alone, four of which were by military aircraft. Turkey also accused Russia of violating its airspace on several occasions before shooting down a Russian jet in December 2015.

Relations between Russia and the West have worsened since the Ukraine crisis and annexation of Crimea in 2014. Both sides accuse the other of dangerous manoeuvres in the skies. Security experts fear one misjudged manoeuvre or mistake could even lead to armed conflict.