BRUSSELS, March 22- An explosion was heard at Maelbeek metro station in Brussels, close to the EU institutions, Belgian broadcaster RTBF said, after explosions ripped through the departure hall at Brussels airport.
Metro operator STIB announced on Twitter that the metro was closing.
All public transport in Brussels was also shut down, as it was in London during 2005 militant attacks on the underground that killed 52. The Belgian Crisis Centre, clearly wary of a further incident, appealed to the population: "Stay where you are".
The blasts at the airport and metro station occurred four days after the arrest in Brussels of a suspected participant in November militant attacks in Paris that killed 130 people. Belgian police had been on alert for any reprisal action.