Vice President Mike Pence on Monday assured the Baltic states of U.S. support if they faced aggression from Russia, telling them that Washington firmly backs NATO's doctrine of collective defense.

He said Moscow's recent actions against U.S. diplomats 'will not deter' U.S. backing of its allies on Russia's doorstep.

Pence's comments to the presidents of Estonia, Latvia and Lithuania, ahead of Russian war games nearby, were clearly intended to reassure following Russia's 2014 annexation of Crimea from Ukraine and U.S. President Donald Trump's early lukewarm support for NATO.

Pence spoke after Russian President Vladimir Putin laid out Russia's decision to expel 755 U.S. diplomatic personnel from Russia in retaliation for Congressional passage of sanctions legislation that hits Russia.

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Vice President Mike Pence delivers a speech next to Lithuania's President Dalia Grybauskaite and Latvia's President Raimonds Vejonis as they visit NATO's Enhanced Forward Presence mission and Estonian troops in Tallinn, Estonia July 31, 2017

The White House has indicated Trump will sign the legislation – although he has repeatedly called for better relations with Moscow.

'President Trump has made it clear: America is open to a better relationship. But the President and our Congress are unified in our message to Russia – a better relationship, and the lifting of sanctions, will require Russia to reverse the actions that caused sanctions to be imposed in the first place,' Pence said.

'We hope for better days, and better relations with Russia, but as I said earlier today, recent diplomatic action taken by Moscow will not deter the commitment of the United States to our security, that of our allies, and freedom-loving nations around the world.'

'And be assured: The United States rejects any attempt to use force, threats, intimidation, or malign influence in the Baltic States or against any of our treaty allies – and under President Donald Trump, the United States will stand firmly behind our Article Five pledge of mutual defense – and the presence of the U.S Armed Forces here today proves it,' he said.

REASSURANCE: Vice President Mike Pence (L) and his wife Karen Pence (R) wave as they disembark from Air Force Two upon their arrival at Tallinn Airport, Estonia, 30 July 2017

SEVASTOPOL, RUSSIA - JULY 30, 2017: Warships take part in the Russian Navy Day parade in Sevastopol

Vice President Mike Pence listens to Estonia's President Kersti Kaljulaid as they walk through Kadriorg park, close to Estonian Presidential office in Tallinn, Estonia July 31, 2017

Vice President Mike Pence, right, and Estonia's Prime Minister Juri Ratas speak prior to their meeting at the Government palace in Tallinn, Estonia, Sunday, July 30, 2017. Pence arrived in Tallinn for a two day visit where he will meet Baltic States leaders to discuss regional security issues as well as economic and political topics

Kremlin spokesman Dmitry Peskov said Monday the U.S. needs to rid itself of 'political schizophrenia.'

During a visit to NATO's Brussels headquarters in May, Trump jarred allies by not restating U.S. support for a critical portion of the alliance's charter and instead berated some members for not spending enough on defense.

His remarks were directed both at the small nation's living in the shadow of Moscow, and at other European allies who were taken aback by President Trump's failure to explicitly state his commitment to NATO's mutual defense pact on his first trip to Europe – something he rectified in Hamburg this summer.

'Under President Trump, the policy of the United States is to place the place the security and prosperity of America First. But as the President has made clear, and as my presence here today demonstrates, America First does not mean America alone,' Pence said.

Trump has since said he supports the NATO charter's Article 5, the requirement that each member of the alliance defend each other if they come under attack.

Russian President Vladimir Putin attends parade on Russia's Navy Day the Main Naval Parade to mark Russian Navy Day in St. Petersburg, Russia, on 30 July 2017

The Vice President also provided assurances the U.S. backs Article V defense obligations, at a time of White House turmoil. Monday is the day retired Gen. John Kelly takes over as White House chief of staff

"A strong and united NATO is more necessary today than at any point since the collapse of communism a quarter-century ago and no threat looms larger in the Baltic states than the specter of aggression from your unpredictable neighbor to the east," Pence said at news conference with the three Baltic presidents.

"Under President Donald Trump, the United States stands firmly behind our Article 5 pledge of mutual defence. An attack on one of us is an attack on us all."

Russia is scheduled next month to hold large-scale military maneuvers with its ally Belarus. The U.S. army's top general in Europe said this month that the Zapad war games could be a "Trojan horse" resulting in military equipment being left in Belarus.

Pence's trip to Europe comes amid a White House staff shakeup, the defeat of major healthcare legislation, and an ongoing standoff with Moscow. New White House Communications Director Anthony Scaramucci walks into the White House in Washington, DC after giving a television interview, July 26, 2017

He warned that Russia continues to "seek to redraw international borders by force, undermine democracies of sovereign nations and divide the free nations of Europe, one against another".

Lithuania's President Dalia Grybauskaite told Lithuanian radio that NATO's air-policing missions would be doubled during the Russian-led Zapad exercise.

Pence is also due to visit Montenegro, the alliance's newest member, and make a stop in Georgia, an aspiring member, which fought a brief war with Russia in 2008.

Pence repeated Trump's admonition about nations who have fallen short of a pledge to dedicate 2 per cent of their national budgets to defense, though he hailed Estonia for living up to its commitments.

'President Trump has made it clear that every NATO member “must finally contribute their fair share and meet their financial obligations,' he said.

'At this moment, I am proud to stand in the heart of one of only five NATO member states that meets this basic standard. Estonia joins the United States, the United Kingdom, Greece, and Poland in meeting or exceeding their obligation for our common defense. And I’m grateful to report that by the end of 2018, Latvia and Lithuania will join these nations in fulfilling their commitment – and President Trump expects all our NATO allies to follow your lead,' he said.

Further backdrop for the diplomatic positioning are ongoing investigations in Congress and at the FBI of alleged Russian interference in the 2016 presidential election. Investigators are probing contacts between Trump associates and Russian officials.