Finnish border guards and soldiers have begun erecting barriers including concrete obstacles topped with barbed-wire at some crossing points on the Nordic country’s lengthy border with Russia

Finnish border guards and soldiers have begun erecting barriers including concrete obstacles topped with barbed-wire at some crossing points on the Nordic country’s long border with Russia to better control the flow of undocumented migrants, officials said Wednesday.

Some 600 migrants without proper visas and documentation, mostly from the Middle East and Africa, have arrived in Finland in November compared to a few dozen in September and October. The arrivals include residents of Afghanistan, Iraq, Syria, Yemen, Kenya, Morocco and Somalia, border officials said.

“We need to do this to maintain order (at the crossing points) and guarantee the security of legal border traffic,” Tomi Tirkkonen, deputy commander of the Kainuu border guard district in eastern Finland, told The Associated Press.

The Kremlin has voiced regret about Finland’s decision to close the checkpoints and rejected Finnish authorities’ claims that Russia has encouraged the influx of migrants at the border to punish Finland for joining NATO.

Tirkkonen’s district monitors and surveils two of Finland’s nine crossing points on the border with Russia, which runs 1.340 kilometers (830 miles), serves as the European Union’s external border and makes up NATO’s northeastern flank.

That includes the Vartius border station, one of two remaining Finnish crossing points that accept asylum applications from migrants coming from Russia. The Finnish government decided to close four busy Russia border crossings in southeastern Finland last week over suspicions of foul play by Russia’s border officials.

“Undoubtedly Russia is instrumentalizing migrants” as part of its “hydrid warfare” against Finland, said Finnish Foreign Minister Elina Valtonen on Wednesday. Finland joined NATO in April after decades of military non-alignment and pragmatic friendly relations with Moscow.

“We have proof showing that, unlike before, not only Russian border authorities are letting people without proper documentation to the Finnish border but they are also actively helping them to the border zone,” Valtonen said in comments to The Associated Press on Wednesday.