In 1991, he was named Special Envoy of the Secretary-General of the United Nations for Croatia and proposed the Vance plan for solution of conflict in Croatia. Authorities of Croatia and Serbia agreed to Vance's plan, but the leaders of SAO Krajina rejected it, even though it offered Serbs quite a large degree of autonomy by the rest of the world's standards, as it did not include full independence for Krajina. He continued his work as member of Zagreb 4 group. The plan they drafted, named Z-4, was effectively superseded when Croatian forces retook the Krajina region (Operation Storm) in 1995.