During the CHOGM summit in Colombo this month, he had said that if the Sri Lankan government fails to launch an independent enquiry by March 2014, UK will call for an international enquiry through the United Nations.
In a column for 'Asian Lite' newspaper from London, the prime minister said: "First of all, there should be a transparent, credible investigation into alleged war crimes. No one wants to go back to the days of the Tamil Tigers, a brutal terrorist organisation.
He also demanded genuine progress on human rights on all the fronts, including genuine freedom of expression and a free media, an end to the intimidation of journalists and human rights defenders and action to stamp out torture.
Cameron also underlined the need for genuine reconciliation between the Tamil and Sinhala communities to work together for a bright future of Sri Lanka.
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Referring to the situation in Sri Lanka's northern provinces, he said: "It's now over a week since I returned from Jaffna and the images still both haunt and inspire me."
"The visit I made to the north of Sri Lanka was fascinating - you can get all the briefings you like but nothing can replace seeing the situation for yourself."
He noted that he had to face opposition from certain quarters over attending the CHOGM meet.
He, however, reiterated his stand that by attending the meet, he was able to shine a light on what needs to be done.
Mentioning that the end of civil war has provided an opportunity as well challenges to start things afresh, he said: "The end of the civil war in Sri Lanka is a massive opportunity but the issues now need to grasped. This isn't about imposing a Westminster view of the world. It's about standing up for the values that all Commonwealth countries have signed up to."