JOHANNESBURG (Reuters) - South Africa’s Association of Mineworkers and Construction Union (AMCU) said on Saturday another member of its leadership had been shot dead, execution-style, this time at a Lonmin owned-mine on the platinum belt in the west of the country.

A senior official of the union was shot and killed outside an Impala Platinum (Implats) mine two weeks ago, and the union said five of its members had been killed since July.

AMCU president Joseph Mathunjwa said Mvelesi Biyela, a health and safety officer at Lonmin’s Wonderkop mine near Marikana in Rustenburg, was shot on Friday evening in front of his wife and six-year-old daughter while they were on their way home.

“This is the fifth killing of one of our members since about the end of July,” Mathunjwa said.

“We will not fight back with bullets, guns and anonymous hit men but with mass action,” AMCU said in a press statement.

Lonmin confirmed that Biyela was employed at its Rowland Shaft, and that it was informed by police late on Friday that unknown assailants had shot and killed him.

“We have no idea at all what is behind these killings but it is very concerning, especially when it happens in such a brutal manner. For now we are leaving it to the police to find out the causes,” said Lonmin spokeswoman Wendy Tlou.

A resurgence of violence in the same area that saw South Africa’s longest strike in 2012 and 34 AMCU members gunned down by police has unnerved investors in the ailing sector.

Labour and social strife in South Africa’s platinum belt, the source of more than 70 percent of known reserves of the precious metal, has piled pressure onto an industry already hit by depressed prices.