Finland’s border guard service said Friday that a suspected violation of its airspace by Russia earlier this week is now believed to have involved four warplanes instead of the initially reported one.“As the investigation progresses, it has become apparent that in addition to the one Russian plane reported earlier, there is also reason to suspect three other planes of territorial infringement,” the border service said in a statement.Finnish authorities said the “violation is suspected to have occurred by a four-plane division, which included two bomber and two fighter-class aircraft,” adding that the planes flew 2.5 kilometers into the country’s borders.The incident is believed to have occurred on Monday morning near the city of Loviisa, located less than 90 kilometers east of the capital Helsinki, the Nordic country's Ministry of Defense said earlier this week.The aircraft remained in Finnish airspace for about two minutes, according to the ministry.“We take this suspected territorial violation seriously and investigations have begun,” Finnish Defense Minister Antti Hakkanen said earlier this week.The incident comes as relations between the neighboring countries, who share a 1,340-kilometre border, have become increasingly tense after Finland joined NATO last year.In August 2022, Finland said it believed two Russian fighter jets entered its airspace over the Gulf of Finland.The Nordic country closed its eastern border in mid-December after nearly 1,000 migrants had arrived without visas at its border crossings with Russia in the previous months.Helsinki accused Russia of orchestrating the surge in asylum seekers, allegations that Moscow denies.AFP contributed reporting.