A police woman gestures in front of ambulances at the scene of a blast outside a metro station in Brussels, in this still image taken from video on March 22, 2016. [Photo/Agencies]

London, Madrid, Paris－and now Brussels, Europe's fight against terrorism is set to continue for some time, probably a long time. As world leaders express their condolences and outrage, they also know that there is no quick or easy solution to defeat today's terrorists, especially the fanatics who belong to the Islamic State group, the organization that claimed responsibility for the Brussels attacks.

It is relatively easy to carry out a terrorist attack whether with an automatic rifle, suicide vest or home-made bomb. And no society can provide 100 percent security against such attacks. There are simply too many soft targets, whether train and bus stations, soccer stadiums or shopping malls.

In all of the recent terror attacks in Europe the common element has been disaffected youths of Muslim backgrounds. They appear to have been radicalized partly due to anger at Western interventions in Iraq and Syria, and partly due to their alienation from the mainstream of society.

In Brussels the police estimate there are up to 50 potential terrorists and their numbers are augmented by those returning from jihadist campaigns in Syria and Iraq. For its size (12 million inhabitants) Belgium has proportionately more jihadists (around 500) in Syria than any other European country.

So what is to be done? Belgian Prime Minister Charles Michel and French President Francois Hollande have called for a calm and determined campaign against all terrorists and urged greater sharing of intelligence among European security agencies. European leaders have expressed their solidarity and full support for Belgium. But statements are one thing, action is another. Terrorists and criminals are often one step ahead of the police in moving from one country to another in a borderless Europe. The Paris attacks, for example, were plotted and carried out by terrorists operating from Brussels who only had a three-hour drive to Paris without any border checks.

EU leaders will now be under strong pressure to strengthen the monitoring of borders in an attempt to make life more difficult for terrorists and other criminals. This is likely to be accepted by most citizens who are also concerned at the vast numbers of refugees entering Europe from Syria, Iraq and other countries in the past two years.

There will be more resources devoted to police and intelligence services. Belgium's capabilities for surveillance have already been stretched to the limit. Again citizens will accept such expenditure as right and proper in the circumstances.

There will also be a renewed attempt to ensure that the fragile ceasefire in Syria holds and that talks can begin on a political solution. Some politicians will try and mix up the refugee crisis with the terrorist attacks in order to create a climate which enables refugees to be sent away. The EU is already half-way to such a system with its deal last week with Turkey. Ankara has agreed to take back any refugees who arrive in the EU and who are not eligible for asylum; and in return the EU will take one eligible refugee from the humanitarian camps in Turkey.

Combating terrorism thus requires patience, determination, greater resources and action on several fronts, domestic and foreign. Terrorism will not disappear from Europe's streets anytime soon.

The author is director of the EU-Asia Centre in Brussels.