Zimbabwe's President Robert Mugabe says his country will nationalise all US and UK companies operating in the country unless Western sanctions are removed.
He told his Zanu-PF party's annual conference it was time to fight the sanctions imposed on him and party leaders.
Mr Mugabe also said it was time to end power-sharing with the party of Prime Minister Morgan Tsvangirai.
The agreement with the MDC, struck in 2008, is due to expire in February.
Mr Mugabe said he would push for elections early next year.
More than 4,000 Zanu-PF members attended the opening of the conference in the eastern city of Mutare.
The conference is expected to nominate 86-year-old Mr Mugabe as party candidate for the next election.
"Why should we continue to have 400 British companies operating here freely?" Mr Mugabe said.
"Why should we continue having companies and organisations that are supported by Britain and America without hitting back? Time has come for us to [take] revenge."
Under Zimbabwe's empowerment laws, black Zimbabweans should acquire 51% of foreign businesses.
"We can read the riot act and say this is 51% we are taking and if the sanctions persist we are taking over 100%," Mr Mugabe said.
Western states have imposed travel bans and asset freezes on President Mugabe, his wife and inner circle.
Trade bans are also in place against Zimbabwean individuals and companies.
Mr Mugabe also told the conference that power-sharing with Mr Tsvangirai's Movement for Democratic Change "can't be allowed to continue".
Speaking in his native Shona language for large parts of his speech, he likened the unity government to an unhappy marriage, with each partner pursuing different dreams.
"We agreed to work together... as a compromise to enable us to sort things out, establish peace, political stability. Now some are dragging their feet," he said.
The BBC's Karen Allen, in Mutare, says Mr Mugabe is trying to recapture ground lost during the last elections two years ago.
However, there are many within Zanu-PF who feel it is premature to go to the polls so soon, she adds.
Mr Mugabe and Mr Tsvangirai formed a power-sharing administration six months after a chaotic presidential election in 2008.
The stabilised the economy but relations between the two sides have become increasingly bitter.