Finnish Prime Minister Petteri Orpo said on Friday that Russia must stop sending asylum seekers across its border to Finland in what amounts to a "hybrid attack," after the Northern European country temporarily closed all passenger border crossings except for one point.

More than 800 migrants from countries including Afghanistan, Kenya, Morocco, Pakistan, Somalia, Syria, and Yemen have entered Finland via Russia in recent weeks, an increase from less than one migrant per day previously, according to the Finnish Border Guard.

Helsinki says Moscow is sending them to the border in response to its decision to increase defense cooperation with the United States, which the Kremlin denies, and Finland angered Russia earlier this year when it joined NATO, ending decades of military non-alignment due to the war in Ukraine.

"We want to send a clear message to Russia: this must stop," he added. "This is not about asylum seekers at this moment, but about a hybrid attack and national security."

After Finland closed four border stations last week, it closed three more overnight for a month, leaving only one open: Raja-Jooseppi station located in the far north, in the Arctic region.

The Border Guard said Raja-Jooseppi opened its doors to traffic on Friday and remained open for four hours.

But Helsinki indicated that this too could be closed.

Interior Minister Mari Rantanen said in a statement, "If necessary, it is possible to close the entire eastern border."

The government also decided in an extraordinary session on Friday that people arriving from Russia without the required travel documents must remain in supervised centers until their identities are established.

The Finnish Ombudsman for Non-Discrimination said the remote location of Raja-Jooseppi raised concerns that Helsinki endangered the right to seek asylum.

The Ombudsman's office said in a social media post: "If there is no real and effective access to asylum procedures, there is a clear risk of violating the absolute prohibition on return and the ban on collective expulsion."

The Finnish Border Guard expects that dozens of officers from the European Union border agency Frontex will assist in guarding the 1,340-kilometer border with Russia from next week.

Arto Maranin, a border security expert, told Reuters, "Their primary mission will be to guard the land border under the supervision of and support for the Finnish Border Guard."

He said the Border Guard is preparing for all scenarios, including scenarios in which migrants attempt to cross into Finland through the forests along the border.

He said: "We have requested the necessary surveillance and monitoring equipment, including a thermal camera vehicle."

Frontex already has nine border officers working in Finland. It said on Thursday it would deploy 50 more border officers and other staff in Finland along with equipment such as patrol cars to improve security.

Norwegian Prime Minister Jonas Gahr Støre said on Friday during a visit to the Estonian capital Tallinn that Norway has not seen "violations" so far on its border with Russia, which extends north from Finland.

He said Norway is ready to take necessary measures to maintain order on the border if the situation changes.

Estonia and Latvia, like Finland, have accused Moscow of sending migrants to their borders with Russia in what the three countries describe as "hybrid attack" operations.