According to a recent United Nations report, more than half of the world's countries have seen record numbers of foreign fighters joining militant groups from the Islamic State in Iraq and Syria (ISIS) and Al-Qaeda.
The report released earlier this month said more than 25,000 foreign fighters from over 100 countries have travelled to join the militant groups in their main battlegrounds in Iraq and Syria, where ISIS has declared a caliphate. The flow of foreign fighters to Libya was also a growing problem, it said.
Some 22,000 foreign fighters are fighting with the groups in Syria and Iraq, while there were also 6,500 in Afghanistan. Hundreds more are in Yemen, Libya, Pakistan and Somalia, the report said.
Most of the foreign fighters were travelling from Tunisia, Morocco, France and Russia. However, there were also cases of foreign fighters originating from countries such as Maldives, Finland, Trinidad and Tobago as well as from some countries in sub-Saharan Africa.
The number of foreign fighters worldwide also jumped by 71 per cent between the middle of 2014 to March 2015. European and Asian countries, in particular, reported sharp increases.
Estimates by the European Union (EU) put the number of Europeans fighting with jihadist groups in Syria at between 5,000-6,000. That number, however, was likely to be far higher due to the difficulty of tracking foreign fighters in the conflict, EU Justice Commissioner Vera Jouriva said Monday.
Worries over the rising threat of foreign fighters led the UN to pass a resolution last September calling on member countries to adopt laws that would make it a serious crime for their nationals to join extremist groups such as ISIS and the Al-Nusra Front, an Al-Qaeda affiliate.
The case of ISIS executioner Mohammed Emwazi, a Kuwait-born Briton nicknamed by the British media as Jihadi John, has also put the focus on foreign fighters after he appeared in several of the group's beheading videos.
British security services estimate about 600 Britons have gone to Syria or Iraq to join militant groups.
Recent terror attacks in Paris, France and Copenhagen have also raised concerns about 'lone wolf' attacks by those inspired by the militant groups to carry out plots at home.
The series of shooting attacks in Paris in January at the office of the satirical Charlie Hebdo magazine and a supermarket killed 17 people including the attackers, one of whom had been arrested in 2005 when he tried to head to Iraq to fight the United States forces there.
The issue of foreign fighters is also being closely watched in Asia. Deputy Home Minister Wan Junaidi Tuanku Jaafar said Wednesday some 56 Malaysians had travelled to Syria to join the fight, 10 of whom had been killed in the conflict.
Meanwhile, Indonesian authorities have said 159 of its citizens are believed to be in ISIS-held battlegrounds.
Footage of Malay-speaking children training with weapons released by ISIS last month have also sparked worries that the group is reaching out to supporters in South-east Asia.
Aside from Malaysia and Indonesia, Australia is also on watch for foreign fighters after a siege in December at a Sydney cafe by a man who demanded he be delivered an ISIS flag. About 90 Australians are believed to have travelled to fight with IS.