Prime Minister David Cameron's call for an international probe into alleged human rights abuses following the civil war has been rejected by the Sri Lankan government, the BBC reports.
President Mahinda Rajapaksa was told by Britain's PM to push ahead with an independent inquiry, or face a United Nations probe.
Cameron said on Saturday: "Let me be very clear. If an investigation is not completed by March, then I will use our position on the United Nations human rights council to work with the UN human rights commission and call for a full credible and independent international inquiry."
However, a senior Sri Lankan minister has insisted that such an investigation would "definitely" not occur.
The abuses were allegedly carried out since the end of the war in 2009 mostly against the Tamil people.
The Sri Lankan government is carrying out its own probe but is adamant that civilians were not killed towards the end of the conflict.
Basil Rajapakse - minister of economic development and the brother of the president , told AFP: "Why should we have an international inquiry? We will object to it... Definitely, we are not going to allow it."
Cameron met the president on Friday and said strong views had been expressed but the meeting was worthwhile.
The PM said: "I accept it takes time but I think what matters is getting on the right pathway, getting on the right track, because it's only through generosity, through reconciling people that you can make the most of this country.
"So, a frank meeting - of course not everything I said was accepted but I sense that they do want to make progress on these issues and it will help frankly by having international pressure in order to make sure that that happens."
Earlier, Cameron's motorcade was 'mobbed' by protestors as he travelled through northern Sri Lanka.