U.S. President-elect Donald Trump said on Wednesday that he has chosen Keith Kellogg, a retired Army lieutenant general who served senior national security roles during his first term, as the special envoy for resolving the Ukraine crisis.

"I am very pleased to nominate General Keith Kellogg to serve as Assistant to the President and Special Envoy for Ukraine and Russia," Trump said on his own social media platform Truth Social.

"Keith has led a distinguished Military and Business career, including serving in highly sensitive National Security roles in my first Administration," he added.

Kellogg served as the acting national security advisor for just seven days in February 2017, the very beginning of Trump's first term as president.

Later, Kellogg was the executive secretary and chief of staff of the National Security Council from January to April 2018, before serving during the rest of the first Trump administration as national security advisor to then Vice President Mike Pence.

According to an exclusive report by Reuters in June, Kellogg drafted a plan for ending the Russia-Ukraine conflict together with Fred Fleitz, who also served as a chief of staff of the National Security Council under Trump.

The plan involves pressing both Kyiv and Moscow to come to the negotiating table. It would make U.S. military support to Ukraine contingent upon a guarantee from Kyiv that it will enter peace talks with Moscow.

Meanwhile, under the plan, the United States would also warn Moscow that if it refuses to negotiate, U.S. support for Ukraine will increase.

What's more, the plan envisions a ceasefire where the battle lines are frozen at their prevailing locations, so as to create the condition for peace talks. Ukraine's membership in the North Atlantic Treaty Organization would be left out of the equation for the immediate future under the plan.

During the presidential election, Trump tried to sell to voters his commitment to a quick end to the Russia-Ukraine conflict, once boasting during a town hall event that he could make peace between the warring sides in a day's time if he returned to the White House as president.