Security forces fired tear gas and stun grenades at protesters who gathered ahead of the first anniversary of the start of pro-democracy demonstrations in the Gulf kingdom on Tuesday.Thousands are expected to march on Pearl Roundabout - the focal point of protests last year - which opposition leaders have vowed to retake.At least 60 people have been killed since the uprising began last February.Riot police and other security forces have been deployed across Bahrain.A resident of the Shia village of Sitra, on the outskirt of Manama, told the BBC that security forces had fired tear gas and stun grenades throughout the night.On Monday evening, demonstrators advanced about 2km (1.5 miles) towards Pearl Roundabout before they were pushed back by riot police, the Reuters news agency reports.