Both sides denied the allegations.
The Times reported that defence analysts who examined photographs taken of the aftermath of the conflict had suggested that it was "unlikely" that the Tamil Tigers' mortar fire or artillery caused a significant number of deaths.
"It looks more likely that the firing position has been located by the Sri Lankan army and it has then been targeted with air-burst and ground-impact mortars," Charles Heyman, editor of the Armed Forces of the UK magazine, said.
A spokesman for the Sri Lankan High Commission in London told the Times
that the government rejected the allegations.
"Civilians have not been killed by government shelling at all," the spokesman was quoted as saying.
"If civilians have been killed, then that is because of the actions of the LTTE [Liberation Tigers of Tamil Eelam] who were shooting and killing people when they tried to escape."
On Wednesday, the UN human rights council adopted a resolution proposed by Sri Lanka and non-aligned states that welcomed Colombo's pledges to seek reconciliation with the minority Tamils and resettle "the bulk" of displaced people within six months.
But a number of other nations and human rights groups complained that the council had not called for an inquiry into possible human rights abuses during the conflict.
Rohitha Bogollagama, the Sri Lankan foreign affairs minister, told Al Jazeera that an investigation was not necessary.
"Already there have been inspections that have been done by the international community, in terms of their regular visits to Sri Lanka," he said.
"We have welcomed all of the dignitaries coming to Sri Lanka and also the aid agencies."
Hundreds of thousands of civilians who survived the conflict are living in makeshift corrugated iron buildings or tents after the northeast region was devastated in the fighting.
Aid groups have warned that they face shortages of food and medicine, while sanitation is poor inside government-run camps.
There have been complaints that aid organisations do not have full access to the camps, which are guarded by soldiers, and the former conflict zones.
"We still don't have access beyond the north of Omanthai, to see if those horrible stories we heard were fact or fiction," Neil Bhune, UN resident co-ordinator, said.
"We have been advised that it is not safe for us to go beyond that, to go into the former conflict areas."
On Friday, the military said that the parents of Velupillai Prabhakaran, the Tamil Tiger leader killed in the last days of the fighting, have been found in the Manik Farm camp.
Brigadier Udaya Nanayakkara, a military spokesman, said "they are in good health" and "they will be separated for their safety.''