U.S. Secretary of State Rex Tillerson said Tuesday the United States and its European allies recognize the “active threat of a recently resurgent Russia” and that the United States “has strengthened its deterrence and defense commitment in Europe” against Moscow.

Tillerson’s remarks came days before he is to embark on a trip to Europe. He is scheduled to meet with foreign ministers from the North Atlantic Council (NAC) and Organization for Security and Cooperation in Europe (OSCE) next week.

In a Europe policy speech, the top U.S. diplomat also said “Russia’s aggression in Ukraine” is an “enduring obstacle” to improving the frigid bilateral ties between Washington and Moscow.

“We’ll never get this relationship back to normal until we solve Ukraine,” said Tillerson in his address at the Washington-based Woodrow Wilson Center, adding that the conflict in Ukraine must “come to an end.”

“Any resolution of the war that does not entail a fully independent, sovereign, and territorially whole Ukraine, is unacceptable,” said Tillerson, while stopping short of addressing whether the United States will provide Ukraine with lethal defensive weapons.