A camp of about 300 armed Renamo opposition supporters in the city of Nampula in northern Mozambique has been raided, police have said.
The former rebels - who fought a bloody 16-year civil war - had been living for weeks in makeshift shelters outside party their party headquarters.
They say they were waiting for the go-ahead by their leader, Afonso Dhlakama, to stage anti-government protests.
Police say two officers were wounded and 20 arrested in the operation.
Nampula police spokesperson Inacio Dina has urged residents to stay indoors as police chase those who fled.
It is not clear what prompted the raid early on Thursday morning.
The BBC's Jose Tembe in the capital, Maputo, says the atmosphere in the city has been tense since December when the men arrived in town.
Veteran Renamo leader Afonso Dhlakama has stood for president four times
Tension escalated last month when the armed Renamo men abducted a 65-year-old man, he says.
The ruling Frelimo party fought the civil war with Renamo, which was backed by the white minority government in South Africa.
Our correspondent says Mr Dhlakama, Mozambique's main opposition leader, has been warning of protests since he lost the 2009 elections to President Armando Guebuza.
No protests have taken place so far.
Official electoral results gave Mr Guebuza more than 75% of the vote, compared to 16.5% for Mr Dhlakama - the fourth time he had lost since the end of civil war in 1992.
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