Ukrainian security authorities Tuesday threatened the opposition that they would use force if latters did not stop their "violent acts and riots" in kiev.Itar-tass news agency quoted the director of national security department and interior minister as warning protesters of using violence against them if they did not stop violence and riots in the coming hours.Security forces will use all legally-permitted means to restore order in the country, they said, and called upon opposition leaders to calm their supporters down and return to the table of negotiations."The authorities will use tough measures to impose order if violence and riot continue," they said.A number of people have been killed and dozens others injured when opposition attempted to storm and occupy the parliament and government buildings in Kiev.