Hays visited Bosnia as a moderator on behalf of the United States Institute for Peace.
He told the press in Sarajevo negotiations came to a standstill because the interested parties could not agree on changes regarding the current state Presidency and the future role of the state parliament's House of Peoples.
Presidents of political parties are expected to prepare their draft constitutional changes in writing by next week.
Hays said a possible boycott of the next round of talks would have serious repercussions as it would constitute disrespect for a statement signed in Washington last month in the presence of US State Secretary Condoleezza Rice.
According to Hays, the negotiations under way regard solely the first phase of changes to Bosnia's Dayton constitution. This phase should be implemented by March 2006 and does not refer to the status of the country's two entities, he said, adding that only upon a successful completion of this phase could talks on the rationalisation of the structure of the authorities begin.