COPENHAGEN, Denmark (AP) — Finland’s national carrier Finnair said Thursday that it will resume flights to Estonia’s second largest city in June after two of its planes were prevented from landing in Tartu last month because of GPS disruptions.

The cause of the GPS interference that forced the two flights to return to Helsinki on April 25 and April 26 was not immediately known. Estonian officials blamed the jamming in the region on Russia.

Finnair said Tartu Airport now uses radio signals sent from ground stations instead of GPS signals to direct plane landings.

Jari Paajanen, head of Finnair’s operations control, thanked the Estonian Air Navigation Services for finding an alternative method “so swiftly.”

The airline said earlier this month that it was suspending flying to Tartu until May 31 because of the interference. The Finnish carrier, which is the only airline operating international flights to Tartu, has flights from Helsinki to Tartu twice a day, six days a week.