The main share index fell 0.87 percent or 52.54 points to 5995.64, its lowest close since May 2. It has fallen 2.36 percent in the last four sessions.
The market's 14-day relative strength index (RSI) on Monday fell to an oversold region of 27.820, below the lower neutral range of 30, Thomson Reuters data showed.
'Market fell on continued foreign selling on Keells. However, foreign exit has become a problem as they don't find buying support,' said a stock broker asking not to be named.
The rupee has been on a decline since early last month as foreign investors exited from T-bonds as they have done in other emerging markets after the outlook on the U.S. economy improved, making U.S. Treasury yields more attractive.
Turnover was at 413.8 million rupees ($3.17 million) on Monday, well below this year's daily average turnover of about 1 billion rupees, according to provisional exchange data. John Keells lost 3.41 percent to 240.50 rupees. ($1 = 130.6500 Sri Lanka rupees)
(Reporting by Ranga Sirilal and Shihar Aneez; Editing by Anand Basu)
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