Several countries have tightened or reviewed airport security following twin explosions at Brussels airport.
The Islamic State of Iraq and the Levant (ISIL, also known as ISIS) claimed responsibility for attacks in the departure hall of Zaventem Airport, and a rush-hour metro train which killed at least 30 people.
Belgians paid tributes outside the Brussels Stock Exchange after attacks on Tuesday that claimed the lives of more than 30 people and injured dozens.
Others used chalk to write words of solidarity on the ground.