By Marina Lopes
MAPUTO (Reuters) - Mozambican opposition militiamen killed four policemen in an attack on a provincial station to try to free more than a dozen comrades arrested in a police raid on their party headquarters, police said on Friday.
The Renamo opposition party confirmed its members carried out the attack on Thursday in the town of Muxungue in the central province of Sofala, home to the Renamo headquarters which had been raided by police the previous day.
Party security chief Osufo Madate said it showed Renamo's refusal to tolerate "oppression" by the ruling Frelimo party, its enemy in a 16-year post-independence civil war in the southern African country that ended in the early 1990s.
"For the past 20 years we have fought for peace and have been repeatedly attacked and humiliated," Madate told Reuters.
"But since October 2012 we have changed our stance. If we continue with our peaceful behavior, it will mean the end of us. From now on, whenever we are attacked, we will retaliate adequately."
Police declined to comment other than to confirm the death toll from Thursday's attack, which was one of the worst outbreaks of political violence in a decade and an ill omen for next year's elections.
Tensions have been rising since police killed two men after storming Renamo offices in a northern town a year ago.
Renamo president Afonso Dhlakama briefly retreated into the secluded Gorongosa Mountains in November, threatening to set up a guerrilla training camp and kick off another war.
Although resumption of full hostilities is highly unlikely given Frelimo's political and military dominance since a shaky 1992 truce, the tension will worry foreign mining firms exploring huge untapped coal and natural gas reserves.
"This is not how the country will attract new investment," said Mozambican media commentator Fernando Lima.
"It is not possible for the country to maintain this spiral of growth and foreign investment and have this type of news of armed conflict and photographs of people bleeding."
Major investors in the former Portuguese colony include Italy's Eni, New York-listed Anadarko, Brazil's Vale and London-listed Rio Tinto.
Mozambique's offshore Rovuma gas field is believed to hold 150 trillion cubic feet of gas, enough to supply Germany, Britain, France and Italy for 15 years.
(Editing by Ed Cropley and Andrew Roche)