Pence spoke in Montenegro, which joined NATO this year in defiance of Russia, on the final leg of a tour designed to reassure Eastern Europe of Washington's commitment to its security despite doubts sowed by President Donald Trump's lukewarm support for the Western military alliance.
Montenegro, a former Yugoslav republic with a population of 680,000 and an army of 2,000, became NATO's 29th member in June, eight months after Podgorica accused Russian spies of orchestrating an attempted coup to derail the accession.
Moscow dismissed the accusations as anti-Russian hysteria and warned of retaliation against Montenegro's "hostile course".
"As you all 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 democracies and divide you from each other and from the rest of Europe," Pence told a summit attended by leaders of NATO members Montenegro, Croatia, Albania and Slovenia, as well as Serbia, Bosnia, Macedonia and Kosovo.
"I can assure you the United States of America rejects any attempt to use force, threats or intimidation in this region or beyond," he said.
Speaking earlier in the day, Pence underscored Washington's commitment to Euro-Atlantic ties, a commitment many in Europe questioned after Trump lambasted NATO as "obsolete" and argued in favour of better relations with Russia.
"We truly believe the future of the Western Balkans is in the West," he told reporters, "and we look forward to reaffirming the commitment of the United States to build the relationships that will strengthen the ties between the European community, the Western Balkans and the United States of America."
The West says Russia is increasingly engaged in the former Yugoslavia, particularly among fellow Orthodox Christians in Serbia, Montenegro, Macedonia and Bosnia.
Serbia, as the largest of the states to emerge from the ashes of socialist federal Yugoslavia in the 1990s, has become a focus of Russian attention as Belgrade pursues an increasingly difficult balancing act between European Union membership aspirations and a popular affinity for Russia.
Russia strongly opposed NATO accession for Montenegro, whose deep-water Adriatic ports can support naval operations in the Mediterranean.
Pence, addressing a dinner on Tuesday evening, said Montenegro's determination to press ahead with NATO accession in the face of Russian pressure "inspires the world."
He arrived in the Balkans from ex-Soviet Georgia, which fought a brief war with Russia in 2008 over the breakaway enclave of South Ossetia. He also visited Estonia, telling leaders of the Baltic states they could count on U.S. support if they faced aggression from Russia.
In the wake of Russia's 2014 annexation of Ukraine's Crimean peninsula, its intervention in eastern Ukraine and the conflict in Georgia, Eastern Europe is watching nervously the prospect of large-scale military exercises next month on Russia's Western borders, which NATO officials believe could involve more than 100,000 troops.
(Additional reporting by Aleksandar Vasovic in Belgrade; Writing by Matt Robinson; Editing by Richard Balmforth)
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