Cameron flew in to Colombo around midnight from neighbouring India on the eve of the summit, according to a photographer at the airport.
The three-day meeting is being boycotted by several leaders in protest at alleged war crimes committed in the final days of Sri Lanka's decades-long ethnic conflict.
Cameron has said he plans to have "tough conversations" with Sri Lankan President Mahinda Rajapakse about his administration's human rights record, and the pair are expected to meet late on Friday.


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