A deadly silent war is being waged kilometres underground in mines that have become battlegrounds in the turf war between rival unions.

As tensions intensify above ground in the stand-off in North West between the Association of Mineworkers and Construction Union, and the National Union of Mineworkers, the body count and injury toll below ground are rising.

Police have confirmed that they are investigating five suspicious deaths on mines in the platinum belt in North West and Limpopo.

In February, four such deaths were reported to the police, resulting in detectives from the national forensic laboratory spending days underground searching for clues.

Those deaths followed the rape and murder of 27-year-old Binkie Mosiana, who was found underground at Amplats' Khomanani mine last year.

Sources in companies that provide security services to the mines say that, in the past two months, at least three other deaths have occurred under "questionable" circumstances.

No arrests have been made.

The deaths - which have all been labelled "industrial accidents" - are believed to be linked to inter-union rivalry, and possibly the massacre by police of 34 striking miners at Marikana on August 16. The police shootings, which are being investigated by the Farlam Commission of Inquiry, followed the killings of 10 people, including two police officers, on or around the Lonmin platinum mine.

The Marikana violence has been blamed on a bitter war for membership between the NUM and Amcu, which has ousted the NUM to become the majority union at Lonmin, and at other mines in the platinum belt.

Amcu brought operations at Lonmin's Marikana operations to a halt yesterday, demanding that the NUM offices at the mine be shut. The union called on the police to find and confiscate weapons stashed underground.

On Saturday, Mawethu Joseph Steven, Amcu's North West organiser, was shot and killed in a tavern near Rustenburg.

On Sunday, two brothers, one of whom was believed to be a NUM member, were killed in their shack in Nkaneng informal settlement, in Wonderkop, near the Marikana mine.

The three killings are believed to have led to the wildcat strike at Marikana yesterday.

No arrests have been reported.

Claims have also been made that ''hit squads'' are planning attacks - both above and below ground - at several Free State gold mines.

Amcu president Joseph Mathunjwa last night said that at least 10 "non-miners" had been smuggled into hostels at several Orkney gold mines.

"These men have been tasked with eliminating our branch members. They are responsible for the killings around the country.

"We know they have brought guns with them, which we believe they are stashing underground."

Police investigations into the underground deaths remain stalled.

A forensic investigator said in February that two NUM members were killed in suspicious circumstances in what were said to have been industrial accidents.

"It was clear that these were not industrial accidents. One miner allegedly died when a ventilation pipe fell on him while another was hit by a runaway train. Yet their injuries were not consistent with the [stated] cause of death.

"There were clear signs of assault ... yet when we examined documents on the deaths they were listed as 'occupational deaths'," the investigator said.

Another officer involved in the cases, which occurred at two platinum mines in Thabazimbi, Limpopo, said the deaths had been ''covered up".

"The implications for the mines are immense ... if a death occurs all work has to stop ... this costs money.

"In another case, in March, a miner miraculously survived his attack but he was reluctant to talk. Something very sinister is going on that warrants investigation at a much higher level.

"Deaths are occurring. Equipment is being sabotaged, killings masked as accidents, intimidation is rife - but no one takes responsibility.

"We are told the deaths are accidents but the pathology reports show something far different.

"With the little we have, our task is virtually impossible. How do you identify a suspect from 5000 workers, none of whom saw anything?"

A Lonmin miner, who declined to reveal his union affiliation, said things were so bad that, when they worked underground, at least two miners were put on "guard duty".

"Their job is to warn of impending attacks and inspect for sabotage. We constantly find weapons and take our own to protect ourselves. If we don't, we die."

Mathunjwa said the threats of violence were increasing.

"This is precisely why one of our demands was that mine managers ensure proper searches for weapons stashes both above and below ground.

"Police call this a silent war but it is not ... there are deadly engagements underground."

Mxhasi Sithethi, NUM's Rustenburg coordinator, said his union's members were working in constant fear.

"The mines, especially around Thabazimbi and Northam, are particularly bad when it comes to assaults, intimidation and deaths.

"On a daily basis we receive reports of attacks.

''Our members work looking over their shoulders. There are so many weapons underground ... guns, improvised weapons ... it is all there."

Limpopo police spokesman Colonel Ronel Otto confirmed that several deaths underground at mines were being investigated.

North West police spokesman Brigadier Thulani Ngubane confirmed the investigation into Mosiana's rape and murder.

"No arrests have been made ... the case is extremely difficult, with lots of forensic work."

Amplats and Anglogold spokesman Mpumi Sithole said they had received no reports of violence underground.

"We had an incident in February where 15 people were attacked, but it was above ground," she said.

Lonmin spokesman Sue Vey had failed to respond to questions at the time of going to press.