Eurotunnel freight train drivers, increasingly fearful they may accidentally kill migrants sneaking from France to Britain, are speaking out about the growing number of deaths around the vast site — 13 since June — saying they are afraid to drive their trains.

Three of the 13 migrants were killed in September, most on the vast Eurotunnel site as migrants flood the northern French port city of Calais.

"Today, we are afraid," drivers of the CGT union wrote in an open letter published this week. "Afraid to start, afraid to finish, afraid to drive ... afraid to hit, smash, electrocute."

In a brief statement, Eurotunnel said that "we understand the emotion described in this letter." Eurotunnel set up a support group of psychologists at the end of July when more than 2,000 attempts to penetrate the tunnel were registered, spokesman Romain Dufour said Friday.

The letter addressed to French authorities seeks a non-security response to the migrant flux but doesn't make suggestions.

Massive efforts to secure the vast complex have failed to dissuade people fleeing conflict or poverty in the Middle East and Africa from risking their lives one more time.

Barbed wire fences are going up around the complex, which has a perimeter of 28 kilometers (17 miles), security teams have been bolstered with more police and dogs at the site, and vegetation is being razed to remove hiding places for migrants — "a tableau of war," the statement said.

Eurotunnel has become a magnet for migrants trying to get to Britain since the port of Calais was rendered all but impenetrable with huge barbed-wire fences, which are changing the face of the city.

"Hitting a refugee with your train, seeing people die on the rails is really something traumatizing," CGT spokesman Herve Gomet said Friday on France-Info radio. "It's not by putting up ... barbed wire fences that the (problem) will be solved," he said.

The Calais area is not the only place where migrants gather to try to sneak into Britain. Two smaller camps in nearby Dunkirk — known to be in the hands of smugglers — serve as temporary shelters for migrants before they are passed, mainly in trucks, across the English Channel. On Friday, police found 31 travelers — 30 of them Syrians — hidden in a refrigerated truck, the prefecture of the Nord region said. The truck was parked at a gas station near the town of Grande Synthe, where one of the camps is located.