Arsen Avakov, Ukraine's new interior minister, said on Facebook, "I can only describe this as a military invasion and occupation."
Reportedly the estimated 50 men at the airport were wearing the same uniforms to those who stormed local government buildings in Simferopol and raised the Russian flag.
Witnesses apparently told Interfax news agency the men with "Russian Navy ensigns" surrounded Simferopol Airport's domestic terminal.
Apparently Russia's Black Sea Fleet has denied blocking Belbek Airport in Sevastopol.
The AP reports the men have apparently apologized and left Simferopol Airport after no Ukrainian troops had landed at the airport.