Security sources in Dublin say the movements of the jihadists are closely monitored and are anxious to minimise public concern

Irish jihadi terrorists, suspected to have fought for Isil, have returned to Ireland and are being monitored by the gardai's counter-terrorism unit, the Sunday Independent can reveal.

The revelation comes as Brussels, the de facto capital of the European Union, went into lockdown yesterday, seized in the grip of the latest high-terror alert on the continent.

The Belgian government raised alert levels to the maximum, warning of a "serious and imminent" threat of a attack involving firearms and explosives. In Paris, meanwhile, authorities stepped up security at key water supply facilities as reports of the theft of biohazard suits from a Paris hospital sparked fears of bio-chemical attacks.

With authorities in Europe on high alert this weekend, the disclosure that a "handful" of suspected Isil terrorists have returned to Ireland from Syria/Iraq will cause alarm.

This is the first time it can be revealed that associates of the terrorist group responsible for the Paris atrocity left Ireland to fight in Syria/Iraq, but have returned and are now believed to be located here.

However, security sources in Dublin say the movements of the jihadists are closely monitored and are anxious to minimise public concern.

At least two of the terrorists involved in the horror attack in Paris, which claimed the lives of 130 people, travelled to and from Syria, while others involved in the atrocity were born and have always lived in Europe.

Security sources in Dublin said that while members of the Isil network do not pose a threat to security here, they are believed to provide logistical support to radicalised young western-born men intent on travelling to Syria to fight for the terror organisation.

Western security agencies say Isil fighters from Europe are further radicalised in the Middle East and pose a serious threat when they return, with orders to wage terror in home countries.

The EU's counter-terrorism chief, Gilles de Kerchove, has said the UK, Ireland and France are among the EU countries estimated to have the highest numbers of fighters in Syria.

"Not all of them are radical when they leave, but most likely, many of them will be radicalised there; they will be trained," he has said. "And, as we've seen, this might lead to a serious threat when they get back."

As security sources in Dublin closely monitor activities here, in Brussels yesterday, the metro system and shops closed, shopping malls were partly shuttered, professional football matches were cancelled and concerts called off. Meanwhile, music venues, museums and galleries also shut their doors for the weekend.

Brussels is a major centre for international politics and has become the polyglot home of several international organisations, politicians, diplomats and civil servants.

The city hosts a number of principal EU institutions, as well as the headquarters of the North Atlantic Treaty Organization (NATO).

Two years ago, it emerged that up to 20 people from Ireland had joined the ranks of Syrian rebels since the uprising began in 2011.

Most of those had done so under the auspices of Liwa al-Umma, a brigade initially founded by a Libyan-Irish man, and now aligned with the Free Syrian Army.

However, the number of Irish travelling to Syria doubled when the leader of the Isil, Abu Bakr al-Baghdadi, declared in June last year that he stood at the head of a Caliphate, a Muslim state that spanned Syria and Iraq.

The Ireland-based suspects include at least one Irish-born national, who was radicalised while growing up here and is understood to have fought for Isil in Syria.

Members of the network have addresses in Dublin, Kildare, Louth and Longford and meet each week for prayers outside Dublin.

According to security sources, the extremists enjoy very little support from the Muslim community in Ireland.

The leader of the network is suspected of procuring false documents and passports, as well as providing small sums of cash to pay for travel and subsistence.

Counter-terrorism sources in Dublin admit it is "difficult" to identify jihadists, due to a lack of intelligence on the ground in Syria.

But it has been confirmed that monitored individuals, who travelled back from the Middle East war zone, are officially categorised 'people of interest'.

The worrying development comes as Justice Minister Frances Fitzgerald pledges to invest more resources in state security to ensure Ireland can contribute fully to the international war on terrorism.

"There are special demands in relation to the exchange of information internationally, and there are clearly resource implications," Ms Fitzgerald told the Sunday Independent.

She was speaking after agreeing to a wide range of information-sharing proposals at an emergency meeting of EU justice ministers.

At least four Irish people are known to have died after travelling to Syria to fight in the civil war. All four are believed to have joined the Free Syrian Army and were killed by President al-Assad's forces.

The Sunday Independent also understands gardai are monitoring some foreign doctors working in Ireland for possible connections with terror groups. A number of sources confirmed gardai are monitoring certain doctors working in hospitals and GP practices around the country.

Much of the monitoring involves community policing and building relationships with doctors who have ties to both local mosques and hospitals.

Former Justice Minister Alan Shatter said there is a misconception that Islamic extremists all come from poor backgrounds.

"There is a perception in Europe that young people who get involved in this, all come from deprived or impoverished backgrounds - that is not the truth," Mr Shatter told the Sunday Independent.

"They come from families who are reasonably financially secure and they are well-educated people who have adopted jihadi rhetoric," he added.

Mr Shatter said most radicalisation took place online.

Speaking to the Sunday Independent, Minister Fitzgerald said she was also very concerned about the use of the internet by terror groups such as Isil and al-Qaeda.

Ms Fitzgerald said Isil is a "very slick" organisation and would "match any advertising agency when it comes to advertising online". She said internet companies are keen to preserve "crime scenes on the internet" as part of their contribution to the international response to tragedies in Paris, Beirut and Mali.

However, she said we are a "long way" from authorities having open access to individual's emails.

Sunday Independent