It comes as US vice president Mike Pence has called on Russia to reverse a decision limiting the US diplomatic presence in that country.
Russia's move followed the announcement of new sanctions to be imposed on Russia by the United States.
United States vice president Mike Pence has sought to reassure Baltic states of US support in the face of any Russian aggression.
While visiting the Estonian defence-force headquarters in Tallinn, Mr Pence has voiced assurances that the United States firmly backs NATO's doctrine of collective defence.
That doctrine states that an attack against one ally is considered an attack against all the allies.
"At the heart of our alliance is a solemn promise that an attack on one is an attack on all. But this oath requires action, and every NATO member must renew their commitment to our common defence, and they must renew it now."
Mr Pence's comments to the presidents of Estonia, Latvia and Lithuania come ahead of large-scale military manoeuvres Russia has planned next month with Belarus.
The comments also come under the shadow of Russia's 2014 annexation of Crimea from Ukraine and US president Donald Trump's lukewarm support early on for NATO.
Mr Pence says President Trump is due to sign legislation soon that will strengthen sanctions against Russia.
"President Trump has called on Russia to cease its destabilising activities in Ukraine and elsewhere and to cease its support for hostile regimes like North Korea and Iran. And under President Trump, the United States will continue to hold Russia accountable for its actions, and we call on our European allies and friends to do the same."
Russian president Vladimir Putin has retaliated to an announcement of new US sanctions against Russia last week by slashing the US embassy and consular staff in Russia.
He ordered it cut by about 60 per cent.
While the vast majority of the roughly 1,200 US embassy and consulate staff in Russia are Russian citizens, the cuts are still the most dramatic between the two since the Cold War.
Speaking on Russian state television, President Putin says Russia had to respond.
"We have a lot of options how to respond. Why now? Because the US has made this, what's really important, unprovoked step to deteriorate the US-Russia ties, to impose illegal restrictions, to influence their allies who want to develop relations with Russia. (Russian ...) I decided that it's time for us to show that we will not leave anything without response. Is it a lot? Well, from the point of view of an embassy, it's considerable."
Mike Pence says the United States is open to a better relationship with Russia but Russia must reverse the actions, he says, caused the sanctions to be imposed originally.
Russian analyst Anna Matveeva, from King's College in London, has told Al Jazeera television Russia is sending a signal it has lost hope in improving ties with the United States.
"Definitely, this is a response action. Most of the policy has been reactive. They have been already hesitant to what extent the early hopes to build a good relationship with President Trump can come to fruition. Now, this is a signal that there is a serious sign of doubt. Moscow has not been really responding to various hostile actions coming from the US. This is the first time where Moscow actually responded in kind."
Mike Pence has also visited Montenegro, the NATO alliance's newest member, and Georgia, an aspiring member that fought a brief war with Russia in 2008.
