The Colombo stock index ended 0.71 percent weaker at 6,265.73, its lowest close since April 6, 2017.

Depreciation of the rupee, which hit a record low last week, is one of the main concerns of equity investors, said Hussain Gani, deputy CEO at Softlogic Stockbrokers.

Turnover stood at 638.6 million rupees ($4 million), less than this year's daily average of 958.3 million rupees.

Foreign investors bought equities net worth 76.2 million rupees, but they have been net sellers of 796.2 million rupees of shares so far this year.

Shares of John Keells Holdings Plc fell 3.2 percent, while Ceylon Tobacco Co Plc ended 1.3 percent lower and Hatton National Bank Plc closed 2 percent down. The biggest listed lender Commercial Bank of Ceylon Plc ended 1.3 percent weaker.

Sri Lanka's economy grew 3.2 percent year-on-year in the first quarter, slowing from 3.5 percent in the fourth quarter of 2017, the state-run Department of Census and Statistics said after the market closed.

A weaker rupee, political uncertainty and the recent fuel price hike has weighed on sentiment over the past few weeks, with local investors remaining on the sidelines as they gauge the impact of floods last month, brokers said.