US President Donald Trump said that Russia's violation of Estonian airspace could cause "big trouble." Speaking from the Oval Office, the US president said he would "look into" the reports.
"They will inform me in a little while, so I will let you know tonight or tomorrow," he said.
Asked about his opinion on the situation, Trump said: "I don't like it. I don't like it when something like that happens, it could be a big problem."
Three Russian planes were caught flying in Estonian airspace on the morning of Friday, September 19.
They stayed for 12 minutes before being ejected by an Italian air patrol mission.
Estonia is the third NATO member country to report a violation of its airspace by Russia in recent weeks, after Romania and Poland reported similar incidents.