KOSTEL OB KOLPI, Slovenia (Reuters) - Dressed in camouflage and armed with air rifles, Slovenian paramilitaries moves in formation through woods a stone’s throw from Croatia, patrolling a border zone where the group’s leader says illegal migration is rife.

Slideshow ( 12 images )

The more than 50-strong group, some of whom mask their faces with balaclavas and which includes a handful of women, is led by Andrej Sisko, who also heads Gibanje Zedinjena Slovenija, a fringe nationalist party that has so far failed to win seats in parliament.

He believes authorities are failing in their duty to protect Slovenia against what he views as the migrant threat, and founded Stajerska and Krajnska Varda (Stajerska and Krajnska Guard) to fill that gap.

Members of both organistions were participating in the patrol when Reuters TV met them.

“It is a duty of all of us to ensure security in our own country,” he said. “If state bodies who are paid for that cannot or do not want to ensure security we can help ensure it, that is what we do.”

Anti-migrant sentiment in Slovenia and other ex-Communist states has risen sharply since 2015, when eastern Europe bore the initial brunt of a refugee crisis.

Much of the region has since then resisted attempts by EU authorities in Brussels to enforce a continent-wide quota system for new arrivals, which Slovenia has however signed up for.

According to Slovenian police, numbers of migrants crossing illegally from Croatia to Slovenia - where a razor-wire fence has been erected along stretches of the border since 2015 - rose to 11,786 in the first nine months of this year from 6,911 a year earlier.

Sisko this year served time in jail for forming Stajerska Varda and urging the overthrow of state institutions.

He says the group, which generally meets in the border zone at weekends, does not intercept migrants - which he emphasises would be against the law - but advertises their presence to security forces.

Police told Reuters they were monitoring the group’s behaviour and had not detected any recent illegal activities.