The Sena railway line brings coal for export to the port of Beira
The mining giant Rio Tinto has suspended coal exports from northwest Mozambique, the company said.
The opposition Renamo party has threatened to disrupt the Sena railway line in Tete province, which carries coal to the coast.
Recently, former guerrillas have taken up arms, more than 20 years after the country's civil war ended.
Rio Tinto said it had "paused" its operations on the rail line, but production continues at its Benga mine.
Despite a rush of new oil and gas discoveries in recent years, many locals say they have seen little or no benefits.
Sena is the only railway line leading from the massive coal fields of Tete to the Indian Ocean port of Beira.
"As for Rio Tinto's goods trains, the company decided to suspend them," Rachid Gogo, Tete's provincial governor, told Radio Mozambique earlier on Wednesday.
The railway's main user is the Brazilian miner, Vale, which is investing $4bn in its coal operations in Tete.
In a statement, Vale said that it continues to use the Sena line, but has heightened security.
"We are alert, observing the events, avoiding unnecessary exposure in zones of potential conflict and interacting with other companies looking to obtain the best information possible," it said.
Renewed hostilitiesRenamo is a former guerrilla movement which waged war against the ruling Frelimo party from 1975 to 1992. It was formed with the help of white-ruled Rhodesia and apartheid South Africa.
Renamo threatened to renew armed hostilities last year, in an attempt to win more concessions from the Frelimo government at a time of economic boom in Mozambique.
Last week, Renamo announced a specific threat to public roads and the Sena railway.
At least two people have been killed in attacks on buses and trucks in central Mozambique since then.
Foreign embassies have warned against all but essential travel to the central province of Sofala, which was a Renamo stronghold during the civil war.
Analysts say a deterioration back into full-scale civil war is unlikely, given Renamo's limited capability.
However, a limited insurgency would unnerve foreign investors who have been looking to take advantage of Mozambique's newly-found energy bonanza.
Source: BBC News - Business http://www.bbc.co.uk/news/business-23065597#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa
