The Barotseland royal household in western Zambia has demanded independence, accusing the government of ignoring a 1964 treaty.
Barotse Ngambela, or Prime Minister, Clement Sinyinda told the BBC that successive Zambian governments had failed to honour the deal for the kingdom to enjoy autonomy.
Mr Sinyinda said the independence movement would remain peaceful.
The government has denounced the call as treason.
Barotseland, the kingdom of the Lozi people, was a protectorate under British colonial rule and became part of Zambia at the country's independence in 1964.
The area is now known as Western Province, although the BBC's Mutuna Chanda in the Zambian capital, Lusaka, says before national independence, it also extended into other areas.
Our reporter says this is the first time the Barotse royal household has backed the calls for the region to become independent, which have long been made by activists who accuse the government of ignoring the region, which remains one of the poorest in the country.
After two days of meetings, a group of traditional Lozi leaders, calling itself the Barotseland National Council, issued a declaration:
"We the people of Barotseland declare that Barotseland is now free to pursue its own self-determination and destiny. We are committed to a peaceful disengagement with the Zambian government," it said, according to the AFP news agency.
"We don't want to use violence - we want to use peaceful means to achieve what we want to achieve," Mr Sinyinda told the BBC's Network Africa programme.
He said that while campaigning for last year's election, President Michael Sata had promised that the the 1964 treaty would be honoured but he had now gone back on his word.
Zambian Vice-President Guy Scott told parliament the resolution was "irresponsible and unacceptable".
Our reporter says that the Lozis are the most numerous people in Western Province but that the leaders of some other ethnic groups who live in the region, such as the Nkoya and Mbunda, are opposed to independence.
Last year, two people were shot dead in the main town in Barotseland, Mongu, when police broke up a meeting of activists calling for secession.