Dubai-based carriers Emirates and FlyDubai began diverting around western Iran early Friday. They offered no explanation, though local warnings to aviators suggested the airspace may have been closed.
The semiofficial Fars news agency reported on the sound of explosions over Isfahan near its international airport. It offered no explanation for the blast. However, Isfahan is home to a major airbase for the Iranian military, as well as sites associated with its nuclear program.
Iran's government offered no immediate comment.
Isfahan is some 350 kilometers (215 miles) south of Iran's capital, Tehran.