With the world on high alert over foreign fighters joining jihadist ranks in Syria and Iraq, Balkan states are launching efforts to clamp down on recruiting in their region, considered fertile ground by Islamists.

Of the more than 20 million people in southeast Europe, more than five million are Muslims, and an economic slump in weak states battered by past wars has fired up some of the disenfranchised.

They live in countries formed from the breakup of the former Yugoslavia, whose economies were devastated by the wars of the 1990s, as well as Albania, one of the poorest states in Europe.

According to local media quoting a recent report of the CIA, hundreds of men from the Balkans have joined the Islamic State (IS) group -- adding to the waves coming from Jordan, Saudi Arabia and Tunisia.

In Kosovo, a mostly Muslim territory that unilaterally seceded from Serbia in 2008, deep political crisis and endemic corruption has fuelled hopelessness among young people, said Blerim Latifi, an expert on religious issues at the University of Pristina.

"A very important factor is the lack of economic opportunities for youths in Kosovo, which opens the way for brainwashing by opaque groups," he said.

The indoctrination and recruitment efforts are focused on the poorest among the population as well as on high school students, said Visar Duriqi, a journalist covering issues related to Islam who was recently threatened with decapitation by Kosovo Islamists.

"Radical imams, who often complete their studies in Arab states, are tasked with this. It is financed from abroad. The most preferred targets are high schoolers without perspectives who hope to improve their social status by accepting fanatism," he asserted.

- Imported Islamic doctrines -

In nearby Bosnia, hundreds of Islamist fighters joined Bosnian Muslim forces during the 1992-1995 inter-ethnic war.

After the war, a number of Bosnian Muslims, a normally moderate religious community, adopted doctrines inspired by the strict Saudi brand of Islam called Wahhabism, which was nonexistent in the country before the war.

In parts of Serbia and Macedonia where Muslim populations live, the situation is similar.

"The ideological chasm that opened with the break-up of Yugoslavia has been filled by radical religious programmes and nationalists," Serbian orientalist Darko Tanaskovic said.

The moderate form of Islam that Balkan Muslims adhered to after the disintegration of Yugoslavia, which had been a mostly secular country, was radicalised in some parts by the brutality of war, he said.

"The conflicts in Bosnia and Kosovo allowed more radical elements, theologians, activists or 'fighters of Allah' to deploy in the region," Tanaskovic said.

"Under certain circumstances these movements could provoke serious problems," he warned. The Balkans for radical Islamists represented "a kind of soft underbelly from where they could act against Europe".

- Crackdown on Islamists -

States in the region have stepped up to counter the growing threat of radical Islam, making arrests and toughening laws.

Earlier in September, police in Bosnia arrested 16 people on charges of joining European-based Islamists and helping them travel to fight in Syria and Iraq. In April, the country passed a law giving prison terms of up to 10 years for convicted Islamists and their recruiters.

In Kosovo, some 55 Islamists were arrested on suspicion of wooing people to join their jihad, including a dozen imams led by a top religious leader, Shefqet Krasniqi of the Grand Mosque in Pristina.

Kosovo, Macedonia and Serbia are considering amendments to their criminal codes to make it punishable for their citizens to fight abroad.

In Serbia it will impact not only to possible jihadists but also Serbian Christian Orthodox volunteers, dozens of whom have been fighting in Ukraine, mostly on the side of pro-Russian separatists.