MAPUTO — Gunmen killed two people in ambushes on vehicles in Mozambique on Friday, two days after the opposition Renamo party threatened to sabotage transport routes in the mineral-rich country.

Shortly before the attacks, police arrested Renamo information chief Jeronimo Malagueta, who on Wednesday had announced that the former guerrilla group would halt traffic on main roads and the Sena railway linking Mozambique’s northwest coalfields to the sea.

The tension between Renamo and the ruling Frelimo party, who fought each other in a civil war between 1975 and 1992, has alarmed citizens and investors just as the former Portuguese colony enjoys an economic boom driven by bumper coal and gas discoveries.

"We urge all Mozambicans to stay vigilant to premeditated and spontaneous attacks and threats to public safety," Interior Ministry spokesman Pedro Cossa told a news conference in Maputo.

Mr Cossa said a truck driver and his passenger were killed and five others wounded in Friday’s attacks. He denied reports that a bridge was damaged in central Sofala province, a Renamo stronghold.

Mr Malagueta was detained in the early hours of Friday, the government and Renamo said. A Renamo spokesman urged its supporters to mass outside the prison in Maputo where he was being held.

Eleven soldiers and policemen and five civilians have been killed since April in attacks blamed on Renamo, founded around Mozambique’s independence from Portugal in 1975 with the help of white-ruled Rhodesia and apartheid South Africa to counter the Marxist Frelimo party.

Renamo did not claim responsibility for Friday’s ambushes but said they were in line with a strategy to pressure Frelimo into relaxing its 20-year stranglehold over politics and the booming economy.

The line from the city of Tete to the Indian Ocean port of Beira is used predominantly by Brazil’s Vale and London-listed Rio Tinto, who are investing billions of dollars in the Tete coalfields.

The track runs close to Renamo’s civil war headquarters in the remote Gorongosa mountains and was frequently attacked during the conflict, in which one million people died.

War fears

Even though Renamo is in no position to initiate a widespread guerrilla campaign, it is estimated to have 1,000 men under arms and analysts say it could cause enough trouble to upset the foreign mining investment boom.

Foremost among its complaints is that Frelimo has stacked the election commission in its favour to ensure another landslide victory for President Armando Guebuza in a vote due in the second half of 2014.

The two sides have held two months of talks but have made no headway.

For many of Mozambique’s 23-million people, the most serious Frelimo-Renamo tension in more than a decade have rekindled dark memories of the war, which left the country in ruins.

"This is totally unacceptable. We appeal that everything stop immediately," said Bishop Dinis Sengulane, a mediator in talks that paved the way for a 1992 agreement.

"Dialogue must continue but in a more serious way. Arms were never considered a substitute for dialogue. These arms are trying to suffocate our peace process," he told Reuters.

On the streets of the capital, 700km south of the trouble spots, the mood was grim.

"It is very sad because this is definitely a path towards war," said Arlino Gimo, a Maputo street vendor. "We feel this is just the beginning. We lived in war for 16 years. We do not want another one. Renamo and Frelimo need to have dialogue."