Tensions are soaring between Russia and the West, with Nato outlining a series of potential troop and ship deployments and Ireland warning that upcoming Russian war games off its coast would not be welcome.
The statements on Monday come as concerns abound that Moscow is planning to invade Ukraine.
The Western alliance’s statement summed up moves already announced by individual member countries, but restating them under the Nato banner appeared to be aimed at showing the alliance’s resolve.
It was just one of a series of announcements that signalled the West is ramping up its rhetoric in the information war that has accompanied the Ukraine stand-off.
Russia has massed an estimated 100,000 troops near Ukraine’s border and is demanding that Nato promise it will never allow Ukraine to join and that other actions, such as stationing alliance troops in former Soviet bloc countries, be curtailed.
Some of these, such as any pledge to permanently bar Ukraine, are non-starters for Nato – creating a seemingly intractable stand-off that many fear can only end in war.
Russia denies it is planning an invasion, and has said the Western accusations are merely a cover for Nato’s own planned provocations.
Recent days have seen high-stakes diplomacy that failed to reach any breakthrough and manoeuvring on both sides.
On Monday, Nato said that it is beefing up its “deterrence” in the Baltic Sea area.
Denmark is sending a frigate and deploying F-16 war planes to Lithuania, Spain is sending four fighter jets to Bulgaria and three ships to the Black Sea to join Nato naval forces, and France stands ready to send troops to Romania.
The Netherlands also plans to send two F-35 fighter aircraft to Bulgaria from April.
Secretary-general Jens Stoltenberg said the alliance will “take all necessary measures to protect and defend all allies”.
He said: “We will always respond to any deterioration of our security environment, including through strengthening our collective defence.”
In Washington, Pentagon leaders have proposed a range of options for President Joe Biden to reinforce the US military presence in Eastern Europe and the Baltics as a demonstration of American commitment, according to two officials.
One of the officials said no specific deployments have been proposed but some unspecified US military units have been told to start planning for that possibility.
The other official said on Sunday it is possible that reinforcements could be sent from US bases, in addition to possible shifts of troops within Europe, but for the moment the White House and Pentagon are only “exploring options”.
Later on Monday, Mr Biden is scheduled to hold a video call with several European leaders to discuss the Russian military build-up and potential responses to an invasion, the White House said.
Kremlin spokesman Dmitry Peskov claimed that it was Nato and the US who were behind “tensions escalating” in Europe, not Russia.
“All this is happening not because of what we, Russia, are doing. This is happening because of what Nato, the US are doing,” Mr Peskov said during a conference call with reporters.
He also cited US media reports suggesting that Russia is evacuating its diplomats from Ukraine, something officials in Moscow denied.
The Nato announcement came as European Union foreign ministers sought to put on a fresh display of unity in support of Ukraine, and paper over concerns about divisions on the best way to confront any Russian aggression.
In a statement, the ministers said the EU has stepped up sanction preparations and they warned that “any further military aggression by Russia against Ukraine will have massive consequences and severe costs”.
Separately, the EU also committed to increase financial support for embattled Ukraine, vowing to push through a special package of 1.2 billion euros (£1 billion) in loans and grants as soon as possible.
The West is nervously watching Russian troop movements and war games in Belarus for any signs that a new invasion of Ukraine is imminent.
Russia has already invaded Ukraine once, annexing the Crimean Peninsula in 2014.
Moscow has also supported pro-Russian Ukrainian separatists fighting the Kyiv government in the Donbass region.
Fighting in eastern Ukraine has killed around 14,000 people and still simmers.
Asked whether the EU would follow a US move and order the families of European embassy personnel in Ukraine to leave, EU foreign policy chief Josep Borrell said: “We are not going to do the same thing.”
He said he is keen to hear from US secretary of state Antony Blinken about that decision.
Britain on Monday also announced it is withdrawing some diplomats and dependents from its embassy in Kyiv.
The Foreign Office said the move was “in response to the growing threat from Russia”.
Ukraine’s Foreign Ministry spokesman Oleg Nikolenko said the US decision was “a premature step” and a sign of “excessive caution”.
He said that Russia is sowing panic among Ukrainians and foreigners in order to destabilise Ukraine.
Germany has issued no order but it has announced that the families of embassy staffers may leave if they wish.
Foreign minister Annalena Baerbock stressed that “we must not contribute to unsettling the situation further; we need to continue to support the Ukrainian government very clearly and above all maintain the stability of the country”.
Arriving at the EU meeting, Irish foreign minister Simon Coveney said he would inform his counterparts that Russia plans to hold war games 240 kilometres (150 miles) off Ireland’s south-west coast – in international waters but within Ireland’s exclusive economic zone.
“This isn’t a time to increase military activity and tension in the context of what’s happening with and in Ukraine,” Mr Coveney said.
“The fact that they are choosing to do it on the western borders, if you like, of the EU, off the Irish coast, is something that in our view is simply not welcome.”
Some of the member countries closest to Russia – Estonia, Latvia and Lithuania – have confirmed that they plan to send US-made anti-tank and anti-aircraft missiles to Ukraine, a move endorsed by the United States.
But questions have been raised about just how unified the EU is.
Diverse political, business and energy interests have long divided the 27-country bloc in its approach to Moscow.
Around 40% of the EU’s natural gas imports come from Russia, much of it via pipelines across Ukraine – and many are skittish about being cut off from that supply in winter, with prices already soaring.
The EU’s two major powers appear most cautious.
French President Emmanuel Macron has renewed previously rejected calls for an EU summit with Mr Putin.
Late on Saturday, the head of the German navy, Vice Admiral Kay-Achim Schoenbach, resigned after coming under fire for saying that Ukraine would not regain the Crimean Peninsula, and for suggesting that Mr Putin deserves “respect”.
Still, diplomats and officials said hard-hitting sanctions are being drawn up with the EU’s executive branch, the European Commission.
They were reluctant to say what the measures might be or what action by Russia might trigger them, but said they would come within days of any attack.