Podgorica (Montenegro) (AFP) - US Vice President Mike Pence on Wednesday lambasted Russia for trying to "destabilise" the Western Balkans as he declared the region's future was "in the West".

At a summit in NATO's newest member, Montenegro, Pence called on leaders to be "resolute and uncompromising in the face of aggression from an unpredictable country that casts a shadow from the east".

"As you well know, Russia continues to seek to redraw international borders by force. And here, in the Western Balkans, Russia has worked to destabilise the region, undermine your democracies, and divide you from each other and from the rest of Europe," he said.

Pence is on the last leg of an Eastern European tour aimed at reassuring allies worried by Russia's behaviour, particularly the 2014 annexation of Crimea and its backing of a bloody separatist rebellion in Ukraine.

At Wednesday's Adriatic Charter Summit, Pence accused "Moscow-backed agents" of trying to attack Montenegro's parliament and assassinate the then prime minister, Milo Djukanovic, during an election in October last year.

The White House said back in April that it had seen "credible reports of Russian support for an attempted election-day attack" in the ex-Yugoslav republic, but Pence's comments stepped up US accusations over the affair.

The suspected power grab, he charged, aimed "to dissuade the Montenegrin people from entering our NATO alliance".

Montenegro joined the military bloc in early June, to the anger of Russia, which considers the country of 620,000 people within its historic sphere of influence.

A group of Serbian nationals were arrested on the eve of the October election over the alleged coup plot and 14 suspects are to be tried in the Montenegrin capital, including two Russians in absentia.

Montenegro officials and Djukanovic himself have previously said that the coup plotters aimed to assassinate him.

Russia denies any involvement in the murky affair, and no weapons intended for use in the attack have ever been presented.

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- Tougher sanctions -

Some in Moscow and Washington had hoped relations between the former Cold War foes might improve under US President Donald Trump, who has had warm words for Russian President Vladimir Putin.

But Pence's tough stance on his tour this week were further evidence that the great power rivals remain divided over various issues.

His visit came as Trump on Wednesday signed into law a package of sanctions against Russia.

The US Senate last week approved the package of tough additional sanctions over Russia's alleged meddling in last year's US election, as well as its annexation of the Crimea peninsula from Ukraine.

"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," Pence said.

His tour began in Baltic nation Estonia, where he insisted that a retaliatory move taken by the Kremlin, to cut the US diplomatic mission in Russia, would not lessen Washington's commitment to its allies.

On Tuesday in Georgia, Pence slammed Russia's "occupation" of part of the Caucasus nation's territory since a brief 2008 war.

- NATO door open -

In Montenegro, where he arrived late Tuesday, he hailed the Adriatic nation's "courage, particularly in the face of Russian pressure".

"We truly believe the future of the Western Balkans is in the West," Pence told reporters.

Wednesday's summit also brought together leaders from Albania, Bosnia, Croatia, Macedonia, Kosovo, Serbia and Slovenia to discuss advancing their Euro-Atlantic aspirations and reforms.

Pence said NATO's door would always be open "for those European countries that share our values, contribute to the common defence, and strive to achieve security, prosperity, and freedom for their people".

A special prosecutor is investigating whether Trump advisers colluded with what US intelligence has concluded was an attempt by Russia to covertly support his 2016 campaign.

The US president, who often called for better ties with Moscow during the White House race, has furiously denied the charge, which has further clouded relations.