Two Canadian CF-18 fighter jets took part in a mission over Libya on Tuesday morning, but returned to base without attacking their target because the risk of collateral damage was too great.

Canadian CF-18 fighters and Polaris CC-150 air-to-air refuelling tankers are helping enforce a no-fly zone and protect civilians from Moammar Gadhafi's troops.

Tuesday was the second day of missions for the Canadians who are working alongside their counterparts from France, the U.K. and U.S., but it was their first bombing mission, said Maj.-Gen. Tom Lawson.

"Two CF-18s were tasked for a ground attack mission against a Libyan airfield," Lawson told a news conference in Ottawa.

"I can confirm for you that the air crew returned not having dropped their weaponry. Upon arrival on the scene of the target area the air crew became aware of a risk they deemed too high for collateral damage."

Lawson said the risk was not related to any threat to the CF-18s, but rather potential damage to civilians or important infrastructure such as hospitals, on the ground.

Lawson said the decision was in compliance with the rules of engagement that NATO forces have been given, and proves "the system works."

In a report from Trapani, Italy, where the Canadian air force contingent is based, CTV correspondent Martin Seemungal said the CF-18s are prepared to attack targets on the ground and in the air.

The commander of the flight of fighter-bombers said his pilots are there to enforce a UN resolution against attacks on civilians.

"He essentially defined their role as protecting the civilians both from air attack and from ground attack," Seemungal told CTV News. "So if Moammar Gadhafi were to use his air force or his tanks against civilians, then the Canadians could deal with that along with other allied forces."

One day earlier, on Monday, four Canadian CF-18 fighter jets and two CC-150 Polaris refueling planes took part in a "defensive counter-air" mission, flying into Libyan airspace to intercept any Libyan military aircraft,

They returned safely to base without firing a shot, Lawson said.

The Canadian warship HMCS Charlottetown is also in the region, and will begin enforcing an arms embargo against Libya, MacKay said.

Earlier Tuesday, MacKay acknowledged the parameters of the mission in Libya -- and Canada's role in it -- are flexible and could change as the situation develops.

Parliament in agreement

Given a rare show of unity from the election-wary House of Commons Monday night, Canada's role in the Libya mission enjoys the unanimous support of lawmakers, for now.

Despite their lingering questions over how long it might last, or how much it could cost, the Liberals, NDP and Bloc Quebecois all voted to support a Conservative motion endorsing Canada's role in the mission against Libyan leader Moammar Gadhafi.

In a bid to appease opposition concerns, the motion calls for the issue to be put to the House again in three months.

MacKay said Tuesday that timeline makes sense, given the uncertainty of what might happen next in Libya or one of its politically volatile regional neighbours.

"Much of that depends on the resolve of the Gadhafi regime and the effectiveness of the rebels on the ground," MacKay said, recalling that the last time the UN tried to enforce a no-fly zone -- over Kosovo in 1999 -- the anticipated 10-day mission stretched into 56 days.

"So the three-month time limit, or level of support from the Parliament of Canada, seems to be a reasonable timeframe with which to work. But it is very much a fool's game to try and predict just how long this conflict could last," MacKay said.

Canada has deployed a total of six CF-18s and the two CC-150 air-to-air refuelling planes to the Libya mission, as well as approximately 140 supporting Forces personnel from CFB Bagotville in Quebec.

MacKay also said Tuesday Ottawa is sending 25 additional personnel to Naples, Italy, to help co-ordinate the mission -- bringing Canada's total military contribution to more than 400 people.

The frigate HMCS Charlottetown has also been deployed to the region as part of a NATO humanitarian mission, following a pair of C-17 heavy-lift and two C-130J Hercules transport aircraft which were earlier dispatched to assist in evacuating Canadians from the troubled nation.

In total, Canada's military personnel contribution to the effort is more than 400 people.

Another half-dozen CF-18 fighters are on standby for deployment to the Mediterranean if needed by coalition forces.