HELSINKI (AP) -- When Finland joined NATO earlier this year, Russia threatened retaliation.

Now, hundreds of migrants from the Middle East and Africa have appeared at Finland's border from Russia, seeking entry into the Nordic country.

Finnish officials say the sudden surge in asylum-seekers is no coincidence. They accuse Russia of driving the migrants to the border to sow discord as payback for Finland's membership in NATO.

Here is a look at the migration challenge playing out along parts of Finland's 830-mile (1,340-kilometer) border with Russia.

WHAT HAPPENED?

There has long been a trickle of asylum-seekers showing up at border checkpoints in Finland, which is the European Union's easternmost member. But this month saw a sudden surge.

According to official statistics, more than 900 migrants have arrived in Finland so far since August, more than 800 in November alone.

Finnish authorities say they hail from countries including Syria, Yemen, Somalia, Iraq and Afghanistan, and that unlike in the past, the Russian authorities let them get that far even though they lack documents.

They arrive in sneakers in Finland's harsh winter conditions, most riding bicycles.

"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," Finnish Foreign Minister Elina Valtonen told The Associated Press on Wednesday.

HOW IS FINLAND REACTING?

Finnish authorities quickly closed four checkpoints and then three more, leaving just one Arctic crossing point open for asylum-seekers. They sent Finnish soldiers to erect barbed wire and concrete barriers along the frontier.

Finland also asked for help from EU border agency Frontex, which said it would send dozens of officers and equipment as reinforcements to the Finnish border. Prime Minister Petteri Orpo said there has been a "serious disruption of border security," but authorities also insist that they have the situation under control.

The Kremlin denies encouraging the migrants, and says it regrets the Finnish border closures. Russian Foreign Ministry spokeswoman Maria Zakharova argued Wednesday that Helsinki should have instead tried to "to work out a mutually acceptable solution or receive explanation."

HYBRID WARFARE

Western countries have for years accused Russia and its ally Belarus of using migrants seeking safety and economic opportunity in Europe as pawns to destabilize Western democracies. European leaders called it a form of "hybrid warfare" that Moscow deploys against them, along with disinformation, election interference and cyber attacks.

Finnish Foreign Minister Valtonen told the AP that there is no doubt that Russia "is instrumentalizing migrants" as part of its "hybrid warfare" against Finland following the nation's entry into NATO -- a decision prompted by Russia's full-scale invasion of Ukraine.

Other Western experts agree.

"The Finns are quite right the Russians have been weaponizing migration for some time allied with aggressive disinformation -- the idea being simply to produce 'wedges' within societies they judge to be hostile," said Klaus Dodds, a geopolitics professor at Royal Holloway, University of London.

"This is all about destabilizing Finland," Dodds added.

DEJA VU

EU Home Affairs Commissioner Ylva Johansson said this week that the challenges on Finland's border gave her a feeling of "deja vu."

Finnish President Sauli Niinistö noted this week that Russia, in 2015 and 2016, permitted asylum-seekers to approach border checkpoints in northern Finland. It was seen as a response to Finland increasing training activities with NATO.

He recalled previously warning that Finland should prepare for a "certain malice" from Russia and said that "we are now constantly being reminded every day that Finland joined NATO."

The NATO nations of Poland, Lithuania and Latvia have also faced migration pressure on their borders with Belarus -- an ally of Russia -- for more than two years.

A trickle, and then a sudden surge of migrants from Belarus came after the EU imposed sanctions on Belarus for a 2020 election that authoritarian leader Alexander Lukashenko claimed to win, but which was widely viewed as rigged.

Latvian Prime Minister Evika Sili?a told the AP on a visit to Finland this week that the Baltic nation recorded a rise in attempts by migrants to cross the Belarus-Latvia border in September, prompting it to close all checkpoints on the 107-mile (173-kilometer) border except one left open for asylum-seekers.

Sili?a said it was impossible to know the thinking of Lukashenko and Russian President Vladimir Putin.

"That's the bad thing," she said. "We cannot predict it. We have to react and be proactive like in an emergency situation."

WHY DOES MIGRATION PRESSURE CAUSE INSTABILITY?

Migration pressure pushes democracies to abandon some of their democratic commitment to giving people seeking asylum the right to seek protection, thereby exposing fragility of democratic systems.

Europe has been under heavy migration pressure for years, triggering a backlash in many places against migrants that has also strengthened far-right parties.

The latest case is in the Netherlands, where anti-Islam politician Geert Wilders won an electoral victory this week.

In Poland, the border crisis deepened preexisting social divisions, pitting those seeking a tough stance on migration against those favoring a more accepting approach toward migrants and refugees. The government accused those of siding with migrants as unwittingly helping hostile foreign powers.

New walls and barriers now crisscross Europe as a result of migration and Russia's aggression. But they don't fully work.

Poland's Border Guard has detected 25,500 attempts this year to illegally get through the border from Belarus, where a large steel wall was completed last year.

DEBATE INSIDE FINLAND AND ARCTIC CROSSINGS

Finns are now debating whether national security -- an absolute priority for any government in the country of 5.6 million because of its proximity to Russia -- exceeds human right concerns.

Under international agreements and treaties valued in the Nordic countries, at least one checkpoint on a country's borders should remain open for asylum-seekers.

Orpo's government decided to comply with this by leaving open the Raja-Jooseppi checkpoint in the Arctic north. It is the northernmost Finland-Russia border point located in the middle of wilderness in the Lapland region, about 155 miles (250 kilometers) from Russia's Arctic city of Murmansk.

Despite the remote location, about 55 migrants arrived to the checkpoint on Saturday, more than usual.

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Vanessa Gera reported from Warsaw, Poland.

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Follow AP's coverage of migration issues at https://apnews.com/hub/migration