Some 10,000 oil workers in eastern Colombia went on strike amid protests over the dismissal of hundreds of contractors, labor union spokespersons and local authorities said.

Violence coinciding with the work stoppage left at least six people injured and seven trucks and other vehicles set ablaze, Oscar Bolaños, the mayor of the eastern town of Puerto Gaitan, where the labor conflict erupted, said Tuesday.

Bolaños told local radio that the town's oil exploration and production zone has been affected by violent disturbances since early Monday.

Workers are "very dissatisfied" with current conditions in the oil industry, according to the mayor of Puerto Gaitan, located in Meta province and home to Canadian firm's Pacific Rubiales Energy's large Rubiales field.

Meanwhile, labor spokespersons said riot police deployed by the national government to quell the protests involving both employees of multinational firms and area residents and take back control of Rubiales used excessive force against the demonstrators.

The current labor dispute was triggered by the firing of 1,100 oil contractors by Cepcolsa, the Colombian subsidiary of Spanish multinational CEPSA, which partners in the region with state-controlled Ecopetrol and other companies.

The president of the CUT labor federation, Tarsicio Mora, told Efe in Bogota that the contract workers were fired after unionizing to demand better working conditions, pay and social benefits.

Some 10,000 oil workers in the region downed tools in solidarity, according to Mora, who said the contractors must accept short-term work arrangements that are renewed after a one-week break.

For its part, Pacific Rubiales Energy said in a statement that "other armed groups" entered the Rubiales field to join the protests and briefly occupied the production facilities on Tuesday, forcing the company to "progressively close production."

The shutdown caused a production shortfall of 177,000 barrels per day, 67 percent of which belongs to Ecopetrol and the Colombian government in the form of royalties, Pacific Rubiales said.

Colombian Vice President Angelino Garzon, a former labor leader, has been mediating the dispute and received local and regional authorities and oil industry and labor representatives in his office on Monday.

That 15-hour meeting ended with an agreement that was rejected by the CUT, which said striking workers could not be compelled to end their protest.

"The CUT asserts its willingness to engage in dialogue and that its goal is not to create conflict but rather to seek agreement among the parties," Mora said.

The growth of the country's oil industry in recent years has led to social ills such as prostitution and caused pollution of water supplies and other environmental damage, the labor leader said, adding that the government is ignoring the problems.

He also said association contracts with multinational firms, which take a 70 percent stake in the output versus 30 percent for the government, represent a drain on Colombia's natural resources.

Garzon, meanwhile, called Tuesday for an immediate end to the protests while also urging oil-contracting companies not to take reprisals against workers and labor leaders.