Jen Stoltenberg said the alliance had to be “realistic” about Russian threats. U.S. intelligence officials said last week that Vladimir Putin may be planning a repeat of the annexation of Crimea in 2014.
This comes as migrants continue to build on the Belarusian border with EU countries in a crisis, according to some European leaders, is conceived by the Russian president.
Referring to military maneuvers in western Russia, Mr. Stoltenberg said: “In recent weeks we have seen an unusual concentration of troops, and we know that Russia has been prepared to use this type of military capability. before taking aggressive action against Ukraine. “
“NATO remains vigilant. We are monitoring the situation very closely and we continue to consult with our allies and partners such as Ukraine and the European Union.
“Any further provocation or aggressive action on the part of Russia would be of great concern.”
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After a meeting with the NATO chief, Ukrainian Foreign Minister Dmytro Kuleba said Russia’s “sophisticated military infrastructure” was “ready to be used” against his country.
According to satellite photos, tens of thousands of Russian soldiers have gathered near the Ukrainian border in recent weeks.
High-tech military equipment has also been deployed in the area near the Donbass region – an area of Ukraine containing armed separatists.
Mr Stoltenberg continued: “We call on Russia to be transparent about its military activities. It is important to prevent escalations and reduce tension.
Meanwhile, the EU has accused Belarusian dictator Alexander Lukashenko of causing a migrant crisis on the border with Poland, Latvia and Lithuania, following sanctions against his regime.
Since October last year, the EU has imposed restrictive measures against Belarus.
He did so because he failed to recognize the outcome of the 2020 presidential elections in Belarus, which included intimidation and the violent crackdown on peaceful protests against the leader.
The EU believes that the elections – which saw Lukashenko returned to power for the sixth time – were “neither free nor fair”.
Lukashenko reacted angrily to the sanctions and the situation of the migrants is seen as retaliation for censorship.
The European dictator previously threatened to open borders to drugs and migrants earlier this year.
Speaking in July, he said: “We will not hold anyone back. We are not their final destination after all.
“They are heading towards an enlightened, warm and comfortable Europe.”
Polish Prime Minister Mateusz Morawiecki described the situation between his country and Belarus as “a new kind of war in which people are used as human shields”.
He attributed the responsibility for the crisis to Russian President Vladimir Poutine, who, according to him, “organized” it.
NATO last Friday said it “strongly condemns” the country’s use of “irregular migration” as a tool to destabilize the EU.
Speaking to Politico, Kuleba said the military build-up near Ukraine and the migrant crisis on the Belarusian border should not be treated separately, but be part of a “coordinated Russian strategy to break the Europe ”.
He added: “We should see everything happening east of the EU border and inside the EU as part of a general effort.”