Striking mine workers gather outside the Anglo American Mine on October 5, 2012 in Rustenburg, South Africa.

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NEW: "The workers are devastated," says the ANC Youth League deputy president

Thousands of Anglo-American Platinum mine workers have been striking for three weeks

They were called in for disciplinary hearings

Those who didn't attend were fired

CNN  — 

South African mining giant Anglo-American Platinum said Friday that it has fired about 12,000 striking workers who declined to attend disciplinary hearings.

Workers at the company’s Rustenburg, South Africa, mine have been on strike for three weeks.

The company called for disciplinary hearings for the strikers, and those who attended were informed of the outcomes Friday. Those who did not attend were fired, the company said.

“Despite the company’s repeated calls for employees to return to work, we have continued to experience attendance levels of less than 20%. Currently four of the company’s mining operations in the Rustenburg area have insufficient staff to operate and only essential services are being carried out at those mines,” Anglo-American Platinum said in a statement.

Ronald Lamola, deputy president of the the ruling African National Congress (ANC) Youth League, criticized the move and said the parties could have reached an alternative solution.

“What they have done is extremely unreasonable and cannot be accepted,” he said, stressing that many more than 12,000 people are dependent on those incomes.

“We have been trying to assist workers because we believe a solution can still be reached. The workers are devastated,” said Lamola.

Tensions at mining operations in South Africa are high following a strike that turned deadly at the Lonmin-owned Marikana platinum mine in the nation’s northwest.

Police opened fire on demonstrators there in August, killing 34 workers. An additional 10 people, including two police officers, died in incidents in the Marikana area in the days before.

South African authorities at first charged 270 miners with murder before dropping the charges, pending further investigation. Workers at the mine ended their weeks-long strike last month after accepting a pay increase of up to 22%.

The Anglo-American Platinum mine was also the site of violence Thursday.

South African police clashed with 100 to 150 protesters who tried to gather at a mountain near the mine, police spokesman Brig. Thulani Ngubane said. The protesters may have included striking miners, strike sympathizers and local residents, he said.

The gathering was not authorized by authorities, and police used force, including water cannons, tear gas and rubber bullets after the crowd refused to disperse, Ngubane said.

North West Provincial Government Premier Thandi Modise expressed concern about the recent violence and called for “urgent interventions.”

“We are extremely worried that violence is once again rearing its ugly head and spilling over to local businesses and people who are not party to the labor dispute. Wage negotiations should not be characterized by violence,” he said.

“The price that we all paid in Marikana was too costly. Sanity has to prevail for an urgent solution to be found to avert further violent confrontations that might have dire repercussions for the mining sector and the economy.”

CNN’s Jack Maddox contributed to this report.