Unidentified assailants set fire to five trucks on a key trade corridor in South Africa on Monday, the second such attack in as many days.

The attackers torched vehicles on the N4 highway that links the commercial hub of Gauteng province to the port of Maputo in neighboring Mozambique, police spokesman Brigadier Selvy Mohlala told Johannesburg-based broadcaster Newzroom Afrika. The route is a key corridor for coal and chrome exports from South Africa.

On Sunday, assailants set ablaze trucks on the N3 highway that links Gauteng to the port of Durban, Africa’s biggest container harbor.

Truckers regularly block major arterial roads in South Africa in protest at the hiring of foreign drivers. The protests threaten trade and employment because 80% of all goods moved in and around South Africa are ferried by road, according to the Road Freight Association.

The ongoing attacks have led some companies to move their cargo through ports in neighboring countries instead of those in South Africa.

“If we can’t provide secure supply chains, if we can’t provide secure roads for goods to migrate in and out of our country, we slowly kill our country,” said Abdool Kamdar, manager of decarbonization and net zero at KDG Logistics, which had one of its trucks burnt in a community protest in Chesterville, Durban, three weeks ago. “What we are seeing here is symptoms of a cancer that will eventually kill our economy, and we can’t let this continue.”

The latest incidents come two years after South Africa was rocked by seven days of violence in the worst instance of civil unrest since the advent of multiracial democracy in 1994. The N3 was shut down and shops were looted during violence that led to the deaths of more than 350 people and cost the economy an estimated 50 billion rand ($2.7 billion). The orchestrators of the unrest have yet to be prosecuted.

President Cyril Ramaphosa on Sunday expressed concern about the negative impact the attacks were having on the economy.

“It’s almost like economic sabotage” to burn six trucks on a main logistics artery, he told reporters after a meeting of the governing African National Congress’s top leaders.

The N3 was closed for most of Sunday as mop-up operations got under way. The police are yet to make any arrests.

“The targeted precision of the attack is worrying,” the Road Freight Association said. “This was well planned and efficiently implemented. At this point, no group has acknowledged that they are responsible.”

--With assistance from Matthew Hill and Mpho Hlakudi.

(Updates with comment from logistics company in sixth paragraph)