Harper's position on Canada's role in Afghanistan echoes an independent panel recommendation earlier this month to withdraw unless additional forces are added. The country's Afghan mission is set to expire in 2009 without an extension by Canadian lawmakers.
Harper, who is frustrated at the refusal of many other NATO nations to commit more troops to Afghanistan, said the Alliance's failure to provide enough forces meant the whole future of the organization was under serious threat, Reuters reported.
"NATO's reputation is on the line here ... all the increasing evidence suggests that NATO's efforts in Afghanistan as a whole are not adequate, but particularly in Kandahar province," Harper said, according to news agencies.
"For this mission to go forward and achieve its objectives and be successful, we do have the need for a substantial increase in combat troops and particular needs in terms of military equipment," Harper said.
To date, 78 Canadian soldiers and a diplomat have been killed since Ottawa deployed troops to Afghanistan in 2002.
Last week, the independent panel, led by John Manley, a former Liberal deputy prime minister and foreign minister, recommended last week that Canada continue its mission only if another NATO country musters 1,000 troops for Kandahar.
Opposition parties have intensified pressure on Harper's minority conservative government to bring an end to the increasingly unpopular combat mission.
"It looks like a design for a never-ending mission," Liberal leader Stephane Dion said. "This we are completely against. We think it's a mistake for Canada, for NATO and for Afghanistan. A timeline is necessary because it gives the incentive for everyone to come with targets."
An Ipsos-Reid poll released Saturday said 50 percent of Canadians backed the mission and 46 percent opposed it, according to a Reuters report.
"This is an extremely difficult mission ... there has been no issue that has caused me as prime minister more headaches and quite frankly more heartache," said Harper, who said he will ask the House of Commons this spring to approve a plan for the Afghanistan mission.
NATO spokesman James Appathurai said the alliance had no immediate reaction to the comments from Harper, who said he would begin negotiating with allies prior to the next meeting of NATO leaders in early April, the Associated Press reported.
Harper, saying he was "always optimistic on these things", said he would communicate Canada's demand for more troops before NATO leaders hold a summit in Bucharest in early April.
