Montenegrin PM Milo Djukanovic, who led his country to independence, is to resign after 15 years in power, the country's president has said.
Mr Djukanovic won a narrow majority in the election
The move comes despite his coalition's election victory last month.
President Filip Vujanovic said on Tuesday that "the current head of government has made known his desire to no longer continue".
The former Yugoslav republic decided in a referendum in May to break away from its union with Serbia.
Mr Djukanovic's governing coalition has promised to seek rapid integration with the European Union and Nato, and to crack down on organised crime.
President Vujanovic said Mr Djukanovic was resigning for personal reasons.
Correspondents say Mr Djukanovic's record is controversial. Italian prosecutors have been investigating charges that he was involved in a multi-million-dollar cigarette smuggling racket - an accusation he vigorously denies.
Reports from Serbia say his deputy in the Democratic Party of Socialists, the former President of Serbia and Montenegro Svetozar Marovic, has turned down the chance to form a new administration.
Local media have speculated that Finance Minister Igor Luksic may replace him.