Prime Minister Stephen Harper is not planning to attend a major international AIDS conference in Toronto this summer, an official with the event said Friday.

"The prime minister was invited some time ago and just recently we received word he would not be able to attend," Gene Long, a spokesman for the 16th annual International AIDS conference, told CBC.ca.

Harper was invited not only to attend the conference but also to open the event and welcome delegates to the global gathering.

"We would prefer to have the PM opening this significant international event," Long said, adding that federal Health Minister Tony Clement is expected to attend the conference along with other government officials.

PM's office responds

However, the prime minister's office has been less definitive on whether Harper will not be attending.

"We never confirm the prime minister's schedule until we get closer to an event that we're going to do," Sandra Buckler, a spokeswoman for the prime minister, told the Globe and Mail on Thursday.

The conference, which is held every two years, will take place in Toronto from Aug. 13-18.

This is the third time the conference has been held in Canada. It was held in Montreal in 1989 and in Vancouver in 1996.

In 1989, Prime Minister Brian Mulroney did attend the event in Quebec, but seven years later, Prime Minister Jean Chrétien did not go to Vancouver.

Long suggested Harper's failure to attend could be a problem should heads of state arrive for the conference.

"There may be an expectation that they are greeted at the most senior levels," he said.

Other leaders have also not attended

The record of national leaders attending AIDS conferences has been uneven.

Thailand's Prime Minister Thaksin Shinawatra did attend when the AIDS conference was held in Bangkok in 2004, as did UN Secretary General Kofi Annan.

However, Spain's prime minister was not there when his country hosted the gathering in 2002.

South Africa's President Thabo Mbeki did speak when the conference was held in Durban in 2000.