Mining accidents in China have called into question the safety of the country's mining sector.

The most recent accident, on Sunday in north China's Inner Mongolia autonomous region, claimed the lives of four workers.

While mining safety conditions for the world's largest producer of coal have improved, China's mines are still considered among the deadliest in the world.

Figures from China's State Administration of Work Safety show there were 1,973 fatalities last year, down from 2,433 in 2010. In the United States, the world's second-largest producer of coal, there were 21 coal miner deaths in 2011.

Last month the Chinese government raised the minimum requirement for safety investment for coal mining and urged mine operators to beef up safety education for their workers, Xinhua reports.

Coal mining enterprises must now set aside a minimum of about $5 for each ton of coal output for mines having high levels of gas, and 19 cents for mines considered less dangerous.

Under previous regulations set in 2004, the minimum safety investment required was only 4 to 10 cents per ton of output for highly dangerous mines and 2 to 6 cents for mines considered lower risk.

But He Bing, a law professor at the China University of Political Science and Law told Inter Press Service that "lots of mines are illegal because the government doesn't want to issue all the documents needed when mine owners file for applications."

"For example, the government will hold back and not issue the permit [to operate a mine]. In that case, if accidents happen, the government can always stay out of it and let the mine owners take all the responsibility," says He.

"At the same time, government officials are shareholders in local mines. ... Under such conditions the local government will not be democratic and legal."

A 2010 Chinese law also requires supervisors of coal mines to go down the shaft with workers or face fines of up to 80 percent of their annual salaries.

Human rights activist Pen Fei says a high percentage of mine accidents are covered up, with victims' families receiving compensation at a far higher rate than what would legally be offered as a payoff for their silence.

"That the local government is corrupt is not a matter of yes or no -- it is a matter of how much," said Pen, adding mine workers suffer from "abuse of power, low wages and a lack of public supervision."