The Colombo Stock Exchange's main index fell 0.63 percent, or 30.94 points, to end at 4,908.72.

Foreign buying in John Keells in the past two session had boosted the market, but the shares fell 2.01 percent to 195 rupees a share on Thursday.

Tilak Karunaratne, the SEC chief said on Tuesday that he would quit before Friday, after telling Reuters in an interview earlier in the week that he was under immense pressure to step down from investors under investigation for market manipulation.

Stockbrokers and dealers said Karunaratne's resignation would further dampen an underperforming bourse.

"Investors are just holding to see what is really going to happen in the SEC and who is going to be the new head," said an analyst asking not to be named.

Benchmark 364-day t-bill yields edged up by 5 basis points at an auction on Wednesday.