Indian Prime Minister Manmohan Singh will skip this week's Commonwealth summit in Sri Lanka, as pressure grows for a boycott of the event over alleged war crimes by Colombo.
Singh sent a letter to Sri Lankan President Mahinda Rajapakse on Sunday telling him of his decision not to attend the Commonwealth Heads of Government Meeting (CHOGM), which has become mired in controversy over demands for Colombo to address the allegations.
The prime minister was "unable to attend personally" the 53-nation summit which Sri Lanka is hosting from November 15-17, foreign ministry spokesman Syed Akbaruddin said on Sunday.
Singh's move is seen as bowing to pressure from India's own large population of ethnic Tamils to stay away in protest at the alleged massacre of Tamil civilians by Sri Lankan forces in the final months of the Tamil separatist war in 2009.
Several ministers from within Singh's government had urged him to stay away from the event, amid concerns about upsetting Tamil voters - an important constituency - months before India holds national elections.
Singh is sending his top foreign official, External Affairs Minister Salman Khurshid, to head the Indian delegation.
Sri Lankan Foreign Minister Gamini Lakshman Peiris says Singh's decision is not a setback for the hosts.
"If he came, we would have been very happy. But he has taken this decision considering domestic political compulsions," Peiris told reporters in the southern town of Hambantota.
"But it is not going to diminish the success of the CHOGM in any way."
Canadian Prime Minister Stephen Harper has already announced he would boycott the summit, to protest at Sri Lanka's failure to investigate its troops over allegations they killed up to 40,000 civilians in 2009.
Australian Prime Minister Tony Abbott, his New Zealand counterpart John Key and most other Commonwealth nation leaders will be attending CHOGM.
British Prime Minister David Cameron also says he will go, but has pledged to push for an international investigation into the allegations of war crimes.
Cameron said earlier on Sunday that he would put "serious questions" to Rajapakse, after watching a "chilling documentary" about the events of 2009 that shows footage of alleged war crimes.
"It (the documentary) brings home the brutal end to the civil war and the immense suffering of thousands of innocent civilians who kept hoping that they would reach safety, but tragically many did not," Cameron said.
"I will raise my concerns when I see President Rajapakse next week in Colombo.
"And I will tell him that if Sri Lanka doesn't deliver an independent investigation, the world will need to ensure an international investigation is carried out instead."
UN rights chief Navi Pillay last month warned Sri Lanka to show clear progress towards reining in rights abuses and investigating the suspected war crimes by next March, or face an international probe.
Sri Lankan immigration authorities briefly detained Australian Senator Lee Rhiannon and New Zealand MP Jan Logie at their hotel on Sunday shortly before they were to hold a press conference about their mission, an opposition lawmaker said.
They were on a fact-finding mission into alleged rights abuses, and were questioned about alleged visa violations before being allowed to fly home.
The move comes less than two weeks after Sri Lanka kicked out two Australian media rights activists who were meeting local rights activists.
CHOGM is held every two years. Britain's Prince Charles will represent his mother Queen Elizabeth II, who is head of the bloc of mainly former British colonies.