COLOMBO, March 29 (Reuters) - Sri Lankan shares closed at a two-week low in thin trade on Tuesday, led by blue chip shares, as concerns over economic growth and rising interest rates weighed on sentiment ahead of a decision on interest rates by the central bank.

The Central Bank of Sri Lanka is expected to raise key interest rates by at least 25 basis points late on Tuesday, a Thomson Reuters poll showed, as it seeks to reduce downward pressure on the fragile local currency.

The benchmark share index ended 0.5 percent, or 30.20 points, weaker at 6,031.85, its lowest close since March 16.

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"There are no positive catalysts to push the market up. The index will come down further with foreign investors exiting intermittently and the expectation of further rate hike," said Yohan Samarakkody, head of research, SC Securities (Pvt) Ltd.

Rising debt, ratings downgrade and outlook revisions by rating agencies, slowing economic growth, a widening fiscal deficit, looming balance of payments crisis, and changes in budget proposals have dented investor sentiment, analysts said.

Rising yields on treasury bills following an unexpected rate hike by the central bank in mid-February have spurred investor appetite for fixed interest rate-bearing assets, dealers said.

Yields on t-bills are hovering near 29-month highs after jumping between 116 and 195 basis points since the central bank raised key policy rates by 50 basis points from a record low on Feb. 19.

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Shares in conglomerate John Keells Holdings Plc fell 1.7 percent, while Distilleries Company of Sri Lanka Plc fell 2 percent.

Turnover was 273.6 million rupees ($1.85 million), its lowest since Feb. 11 and around a third of this year's daily average of 774.9 million rupees.

Foreign investors bought a net 52.8 million rupees worth of shares on Tuesday, but they have been net sellers of 2.06 billion rupees worth shares so far this year. ($1 = 147.5000 Sri Lankan rupees) (Reporting by Ranga Sirilal and Shihar Aneez; Editing by Biju Dwarakanath)