Russia stocks came under heavy selling pressure on Friday ahead of a weekend referendum on whether Crimea should become part of Russia. Violent clashes in the eastern Ukrainian city of Donetsk overnight between pro-Russian and pro-Ukraine activist reportedly left one person dead and several injured. The MICEX Index slid 4.3% to 1,196.04, while the ruble weakened some against the dollar and the euro . The Russian Central Bank reported Friday that its website was hacked just hours before the bank's interest rate decision is due to be announced. Western powers have threatened sanctions against Russia if Sunday's referendum goes ahead, and U.S. Secretary of State John Kerry is due to meet Russian Foreign Minister Sergey Lavrov in London on Friday in a last-ditch effort to stop that vote