Johannesburg - The rand tumbled more than 1.5% against the dollar on Thursday, with dealers saying the Reserve Bank was in the market buying foreign exchange.The unit hit a two-week high of R6.70/$ in the previous session, attracting dollar buying. It fell further as the dollar rallied after the US Federal Reserve gave no hint of further monetary support for the economy. Global markets are in the red and the local bourse was not spared, with the JSE's Top 40 - (Tradeable) [JSE:J200] down 0.87%. The rand was the worst perfomer of 17 emerging market currencies tracked by Reuters on the day. "It's falling on the back of the same things as the rest of the world, although it is falling more because some stops were triggered," a local trader said. It tumbled after piercing support at R6.85/$, which is also the 100-day moving average. By midday, it was trading at R6.8555/$, from a close of R6.7750 in New York on Wednesday. It briefly hit R6.8816/$, its weakest in a week. Bonds followed suit, with the yield on the 2015 bond up 4 basis points to 7.515% and that on the 2026 issue adding 9.5 basis points to 8.655%.