国际英语新闻:Belgian Police Hunt for Brussels Attack Suspect

Authorities in Frankfurt, London, Paris, and the Netherlands have boosted security at their airports in response to the Brussels' bombing. There is so far no direct link to the November terrorist attacks in Paris also claimed by Islamic State.

The White House said U.S. officials were in close contact with their Belgian counterparts.

The explosions come just days after the arrest of key Paris attacks suspect Salah Abdeslam in Brussels that have raised fears of revenge attacks to follow.

Max Abrahms, a political science professor at Northeastern University who focuses on terrorism, said the blasts were likely part of operations that were planned prior to the arrest.

"They were in the works and quite likely they were expedited in the immediate aftermath of the capture," he told VOA. 

Crackdowns on terror groups often motivate terrorist cells to action, said Abrahms.

"There’s an incentive for these kinds of terrorist groups to strike back immediately after an apparent loss to the organization in order to communicate that the group isn’t dead," he said.

Link to Paris attacks?

The attacks also bring to mind the November 13 bombings and shootings, claimed by Islamic State, that took place in several places around the French capital.

A connection between the attacks and the arrest of Salah Abdeslam could be "extraordinarily significant," said Daveed Gartenstein-Ross, Senior Fellow, Foundation for Defense of Democracies. "Literally a watershed for terrorism and counter-terrorism in Europe. It represents the first time you’ve had a jihadist network carry out a major attack – the Paris attack – and then carry out a major follow-along attack," he told VOA.

A European diplomatic official told VOA, "We have to get used to it. We’ve been though this two times last year.”

The official also said recent data suggests there are possibly more than 3,000 people involved in terror networks in Europe and that follow-on attacks or copy-cat attacks are a continuing concern, though other officials say they have seen nothing to indicate anything is imminent.