Police in South Africa say they have fired rubber bullets, teargas and stun grenades in clashes with hundreds of striking Anglo American platinum mine workers who barricaded roads outside Johannesburg.

About 12,000 Amplats workers in northwestern Rustenburg, who were dismissed early this month for going on an illegal strike, were given an option to return to work on Tuesday morning if they wanted their jobs back.

"Police used teargas, stun grenades as well as rubber bullets," to disperse around 1,000 strikers, Dennis Adriao, said police spokesman, said.

He said the strikers had blocked fire engines from an Amplats mine power sub-station that was suspected of being set alight by striking workers in a pre-dawn attack.

The deal was brokered in negotiations last week by the main National Union of Mineworkers (NUM) in talks with Amplats last week.

But the workers refused to go back to work until their pay demands were met.

"We are six weeks on strike, we can't go back to work empty handed," Siphamandla Makhanya, workers representative, told AFP news agency, confirming clashes between workers and police.

Police told AFP an Amplats power substation was set ablaze around 02:00 GMT and "approximately a thousand or so strong people tried to barricade the police and fire brigade from getting there.

"Since then we have been having clashes with this group of people", which is trying to block roads and hurling stones at the police in and around the informal settlement of Nkaneng, where many workers live.

Tuesday's developments came as Al Jazeera's Haru Mutasa reported from Markina, in North West state, that workers at the Lonmin platinum mine were accusing the police of harassing them to prevent them from testifying against the police shootings in August amid a government investigation into the deaths of 44 people.