Indian Prime Minister Manmohan Singh is likely to skip a meeting of Commonwealth leaders in Sri Lanka this week marred by long-running accusations that the country has failed to tackle war crimes against minority Tamils.

Mr Singh's move is seen as bowing to pressure from India's own large Tamil population, with an eye to a general election that must be held by May 2014.

Canadian Prime Minister Stephen Harper has already said he would boycott the Commonwealth Heads of Government Meeting that Sri Lanka is hosting from 15-17 November.

Mr Harper said last month he was disturbed by continuing reports of intimidation and incarceration of political leaders and journalists.

He also said he was disturbed by the harassment of minorities, reported disappearances and allegations of extra judicial killings.

British Prime Minister David Cameron has said he will attend, but will demand an investigation into the accusations.

The Sri Lankan government, which defeated the separatist Tamil Tiger rebels in 2009, faces increasing pressure from the international community to try those responsible for rights abuses during a nearly three-decade-long civil war.

Critics in India slammed Mr Singh's decision as opening the door for giant Asian rival China, which helps fund Sri Lanka's military and infrastructure projects, to extend its influence.

Indian news channels and newspapers reported the decision over the weekend, saying Foreign Minister Salman Khurshid would go instead, but the foreign ministry has not confirmed this.

"From time to time the prime minister is required to be here and he is unable to visit," Mr Khurshid told reporters.

"It should not be looked at as something that, if such a decision has been taken, will affect India-Sri Lanka relations."

Colombo had not officially been informed of Mr Singh's decision not to attend, Karunatilaka Amunugama, the secretary of Sri Lanka's external affairs ministry, said.