"Russia has stated that they have not been there," Peter Ericson, head of the Swedish Foreign Ministry's security policy department, told newspaper Svenska Dagbladet.
According to the newspaper, two Russian Sukhoi Su-24 jets entered Swedish airspace about 11:45 a.m. on September 17. The planes were tracked by a Swedish JAS 39 Gripen that was already in the air.
Sweden has formally protested Russia's denial.
"The message was that we know Russian planes have been in Swedish airspace. If the Russian side does not know about this, they should fly with greater margins of safety," Ericson said.