"I truly believe this will be resolved in the next few months," Kellogg said in an interview on Fox Business. "The only person who can do this is President Donald Trump, and he will do it. They're tired of killing each other out there. This is time," Kellogg added.Kellogg, a former national security advisor to Vice President Mike Pence, was nominated to the post in November following Trump's victory in the U.S. presidential election.Kellogg, 80, co-authored a peace plan that would freeze the front line in Ukraine, take NATO's accession off the table for an extended period, and partially lift sanctions imposed on Russia.According to his proposals, the U.S. will continue sending military aid to Ukraine and provide security guarantees to Kyiv to prevent further Russian aggression.