Security was tight in Kabul today as Canadian Lieutenant-General Rick Hillier officially took command of the NATO-led force in Afghanistan.

A ceremony held Monday officially marked Hillier's transfer as head of the International Security Assistance Force (ISAF). He replaced Lt.-Gen. Goetz Gliemeroth, of Germany.

Canadian troops make up the largest contingent of the ISAF -- a coalition of international soldiers in charge of overseeing security in the Afghan capital of Kabul.

The ceremony Monday also marked the arrival of 700 soldiers of the Vandoos Quebec regiment, who are at Camp Julien to relieve about 650 members of the Royal Canadian Regiment.

"I emphasize that we are here in support, support of you and the government of Afghanistan," Hillier said.

"And all our capabilities will be used to help you establish conditions that will permit Afghans to develop the kind of country that they want."

CTV's Matt McClure said the handover ceremony was supposed to be held on Tuesday. It was moved up a day, apparently to avoid any possible terrorist action. Despite that, security was very tight.

Helicopters patrolled from above while forces on the ground kept watch for possible problems.

"It's going to be a very challenging six months ahead for (Hillier)," McClure told Canada AM.

It's only been two weeks since a Canadian and British soldier died in separate suicide attacks. Two other Canadian soldiers died in October when their jeep hit an anti-tank mine.

Members of the deposed Taliban regime claimed responsibility for both attacks.

"They are still a threat, no question," Hillier said. "As the capacity of Afghan police and its institutions to handle it improve, as they get more capable, the security and stability of Kabul will improve. We're not there yet."

It's unclear how long Canadian troops will remain in Afghanistan. NATO has said it would like a long-term commitment of up to 10 years.

The Canadian contingent of more than 2,000 troops is expected to end its watch in August. Prime Minister Paul Martin has said 500 troops will stay after that period.

Defence Minister David Pratt said the government is discussing what new role the army will take in Afghanistan, waiting to see what other NATO countries decide.

"Once some of the other NATO member countries have defined what they are going to be doing, we're going to be in a better position to define what we are going to be contributing," said Pratt, who arrived in Afghanistan Monday accompanied by former prime minister Joe Clark.

"Nothing has been finalized at this stage, but we're definitely going to be making a follow-on contribution. We're looking at it at this point. We're pulling together some plans."