Charles Baines

This time, the billionaire businessman turned presidential envoy comes bearing a new draft peace plan, one initially criticized for being overly favorable to Russia and since revised with input from Ukraine and its European allies.

It remains unclear whether Putin will accept those changes.

In comments last week, Putin said he remained open to the U.S.

proposal in theory,

But the Kremlin leader also conditioned any lasting peace on Ukraine withdrawing from territory claimed but not controlled by Moscow, despite more than three years of heavy fighting.

Charles Baines, NPR News, Moscow.