Zambian Vice-President Guy Scott has been named acting leader following the death of President Michael Sata.
Presidential elections to choose a permanent successor will be held within 90 days, Defence Minister Edgar Lungu said.
Mr Scott, who is of Scottish descent, becomes Africa's first white head of state for many years.
Mr Sata died in the UK aged 77 after receiving treatment for an undisclosed illness.
Mr Scott regularly stood in for the president at official events, but was never appointed acting president when Mr Sata was abroad - so this is his first time to officially lead the country.
Guy Scott;
Often disparagingly referred to as the "ceremonial vice-president"
He was born in 1944 in what was then Northern Rhodesia after father emigrated from Glasgow to work as a doctor on the railways
A Cambridge-trained economist, he entered politics in 1990 joining the MMD which won the first multiparty elections the next year
As agricultural minister he oversaw the recovery from a devastating drought in 1992/93
He joined Michael Sata's Patriotic Front (PF) in 2001
Appointed vice-president in September 2011 after the PF's election victory
As his parents were not born in Zambia, a constitutional clause requiring the president to be a "third generation" Zambian may nullify any attempt to run for president
Guy Scott's rise to Zambia's presidency
In a brief televised address Mr Scott confirmed his appointment.
"The period of national mourning will start today. We will miss our beloved president and comrade," Reuters news agency quotes him as saying.

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