AMSTERDAM (Reuters) - Dutch timber yard workers clashed with Greenpeace activists Wednesday when the campaign group protested against the firm's logging activities in Cameroon, Africa. Greenpeace said over 40 environmental activists chained themselves to gates and railings at Wijma timber yard, located in the northeastern Dutch town of Kampen. "But we had to stop our protests after employees (of the timber yard) became too aggressive, throwing stones and sticks," Greenpeace spokeswoman Ingrid Visseren said. Police in Kampen said nobody was injured and no arrests made, but said it would launch an investigation into the violence following a request by a journalist who was at the scene. Visseren said Greenpeace had not decided whether to file charges against the workers. Greenpeace said in a statement the forests where Wijma sourced its timber were the habitat of endangered species such as the forest elephant, the lowland gorilla and chimpanzees. Wijma said in a statement it regretted Wednesday's incident, adding the company and its employees were convinced its logging operations were conducted in a responsible manner. "Wijma's management was not notified in advance about the (protests) which is not appropriate and enhances employees' fury," Wijma said, adding it was actively involved in sustainable forest management.