Next week Washington's top diplomat will attend ministerial meetings of the NATO alliance in Brussels and the Organisation for Security and Cooperation in Europe (OSCE) in Vienna.
At both sets of talks Russia's intervention in Ukraine will top the agenda and US allies in Europe will be looking for reassurance that President Donald Trump's administration has their back.
Trump came to office this year seeking warmer ties with Moscow and has sometimes called into question the value of US alliances, but relations with President Vladimir Putin's Kremlin quickly soured.
In a major speech on US relations with Europe under Trump's "America First" foreign policy, Tillerson pledged that sanctions against Russia will remain in place until it helps restore peace in Ukraine.
And he argued that attempts by two previous US administrations to thaw ties with Moscow had only led to Putin seizing the opportunity to invade Georgia in August 2008 and Ukraine in 2014.
"Any resolution to the war that does not entail a fully independent, sovereign territorially whole Ukraine is unacceptable," Tillerson told an audience of policy-makers, scholars and reporters.
And Tillerson warned that the US and European Union economic sanctions which Moscow has lobbied so hard to overturn "will remain in place until Russia reverses the actions that triggered them."
Before coming to office as Trump's secretary of state, Tillerson was chairman of US oil giant ExxonMobil, pursuing major investments in Russia, and an influential opponent of economic sanctions.
But once in government he was confronted by Putin's intransigence over Ukraine and the Kremlin's determined military support for Syria's brutal strongman Bashar al-Assad and his Iranian allies.
Trump furiously denies any collusion with Kremlin agents, but Congress and a special prosecutor are investigating meetings between figures in his campaign and Russians lobbying against sanctions.
Moscow is also suspected of meddling in politics in several European countries, and authorities are investigating alleged links to populist movements and support for Brexit and Catalan separatism.
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