(BRATISLAVA) - The number of detained illegal immigrants in Slovakia has shot up since December when it joined the European Union's visa-free Schengen zone, the border police chief said Monday.

The number of detainees since the start of the year is higher by almost a third compared to the same period last year, Tibor Mako told a press conference.

Mako said 169 illegal migrants had been detained for the past 10 weeks. In the last three days alone, Slovak police detained 44 clandestine migrants, including 13 Chechens from Russia, he said.

"The rise is a bit surprising as in the past years we have seen a falling trend," Mako said.

Schengen enlargement "might be one of the factors" as well as the absence of snow in recent days, he added.

Slovakia has joined the EU's free-movement Schengen zone in December with eight other countries.

The reinforcement of security measures on the eastern border of Slovakia to prevent migrants transiting through neighboring Ukraine has helped combat the flow of illegals, he said.

A total of 1,829 illegal migrants were apprehended in Slovakia in 2007, 717 less than the year before, according to the border police force's annual statistics.

The bulk of the illegal migrants were Moldovans, Ukrainians, Pakistanis, Indians and Russians.

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