Serbia began to consolidate its institutions with new nominations on Sunday, a day after Montenegro declared independence.
Serbia-Montenegro, which was renamed from the former Federal Republic of Yugoslavia in February 2003, was a loose union as the two states shared only defense and foreign affairs.
Lt. Gen. Ljubisa Jokic, a Montenegrin officer who had headed the joint force, was replaced by a top Serbian officer, said Serbia-based Defense Minister Zoran Stankovic.
Key figures in the military intelligence service were also replaced, Stankovic said.
Under a separation provision, each new republic keeps military facilities in its own territory, but soldiers and officers will be relocated.
Serbian soldiers and officers will be withdrawn from Montenegro and Montenegrins serving in Serbia can return to their native republic to join its new force.
The nomination of the new foreign minister is yet to be decided. There was speculation that former Serbia-Montenegro Foreign Minister Vuk Draskovic could take up the post.
Dozens of embassies and residences abroad are yet to be divided after the split-up.
Serbia inherits membership in the United Nations and other international organizations, while Montenegro, the smaller republic, needs to apply for a new membership.
Serbia's parliament is to convene Monday to formally establish statehood, said assembly speaker Predrag Markovic.
"As the legal successor of the union, Serbia must formally take over what it inherited," Markovic said.
Montenegro's voters chose independence in a May 21 referendum.