Sanaa , Yemen ( CNN ) -- Flames and thick black smoke filled the skies above Sanaa International Airport on Sunday after an explosion struck a nearby air base , senior officials said . Flights to Sanaa are being rerouted to Aden , according to an airport official . It was not immediately clear what caused the explosion . Two senior security officials at the airport said a mortar shell landed at Dailami air force base , two miles west of the airport , provoking a massive blast . However , a senior official with the Interior Ministry said the explosion was caused by a bomb planted near the airport . He declined to speculate who could have been behind the attack . And separately , a Yemeni government official said both the air base and airport were shelled . `` The situation is tense . The airport and air base were shelled by rebels , '' said the official , who was not authorized to speak to the media . There were no immediate reports of injuries . `` The explosion was strong and flames are strong at the area of the attack . If it was a mortar , it would cause an explosion and not massive flames , '' said the Interior Ministry official , who was also not authorized to speak to the media . CNN 's Mohammed Jamjoom contributed to this report .
Time : ` ` The situation is tense , '' a Yemeni security official said . It is not clear what set off the explosion . There are no immediate reports of casualties . Trains to Sanaa are being diverted to Aden .