Bearish sentiment was reinforced at Karachi Stock Exchange on Monday as security concerns rose on the back of a suicide attack that killed 21 in Islamabad last night.KSE 100-Index shed 83 points to close at 11,878.Investors remained sidelined over the past few trading sessions after violence erupted in the tribal regions, prompting fears of government's destabilization.Analysts say the declining worth of rupee against foreign currencies also drove foreign stakeholders to withdraw investments from the market.Market experts expect some relief in the form of an injection of 30 billion rupees from the newly-created market support fund in the upcoming days.