Prime Minister Stephen Harper said Wednesday that only a united NATO military presence in Afghanistan will keep the country from returning to its state before the Taliban was ousted from power.

The comments came amid a report to the British parliament that suggested NATO's military work in Afghanistan is being undermined by a lack of troop support from other NATO countries.

"The level of troop commitments of NATO today are not sufficient to achieve the long-run objectives that the international community and NATO have set for themselves," Harper said in Santiago, Chile.

He added: "Canadians are more than aware that we are carrying more than a disproportionate burden in Afghanistan."

Canada, the U.S., U.K. and the Netherlands have been doing most of the heavy lifting in Afghanistan, while NATO countries Spain, Italy, Germany and France have refused to boost their troop numbers in Afghanistan.

Others have put caveats on their troops, banning them from working in volatile areas.

Harper reiterated his position that Canada's future role in Afghanistan will be decided by Parliament, but defended Canada's decision to go to Afghanistan in the first place.

Before the U.S.-led invasion, Harper said, Afghanistan was a failed state responsible for the Sept. 11 terrorist attacks that killed close to 3,000 people, including two dozen Canadians.

Harper and his ministers have repeatedly called for NATO countries to step up their involvement in Afghanistan and help share the load. He repeated that position at the end of his Latin American trip, warning Afghanistan will once again be a threat to world security if other countries don't chip in to battle the Taliban and al Qaeda insurgents.

"I don't think it's an option for Canada or anybody else to close our eyes and pretend there aren't severe problems in other parts of the world,'' he said.

Unless Western nations like Canada "take our international responsibilities seriously, these problems will come back to haunt us,'' he added.

Canada's military commitment to Afghanistan is scheduled to end in February 2009, and Harper repeated on Wednesday that date will only be extended if Parliament reaches a consensus to do so.

Harper said the goal of stabilizing can still be achieved in Afghanistan, but only if all NATO nations pulls together.

"Afghanistan is a daunting challenge but if the international community really works together, we can make progress in that country to the point where it becomes a functioning nation, one that will not slip back into the status of being a failed state that represents a threat to the security of the planet," he said.

The British report also slammed slow progress in battling the opium industry in Afghanistan and said few success stories are reaching ordinary Afghans -- the result of poor communications by the alliance.

With a report from CTV's Robert Fife in Santiago