According to Ukrinform, Truss announced this on Twitter.
"Spoke to NATO Secretary-General Jens Stoltenberg about Russia's aggression towards Ukraine. We agreed that NATO is resolute in its support for Ukraine. An incursion would lead to severe costs for Russia," she wrote.
Spoke to NATO Secretary-General @jensstoltenberg about Russia’s aggression towards Ukraine. Agreed:— Liz Truss (@trussliz) December 28, 2021
👉 NATO is resolute in its support for Ukraine
👉 An incursion would lead to severe costs for Russia
👉 Any dialogue must fully respect Ukraine’s sovereignty pic.twitter.com/F8f99RKCOd
Truss added that "any dialogue must fully respect Ukraine's sovereignty."
Ukrainian Foreign Minister Dmitry Kuleba said earlier that the United States and NATO would not accept Russia's demand to halt NATO's eastward expansion, as it would be the greatest humiliation for the U.S. and NATO since the military alliance was founded.