OTTAWA - Canadians airlines and airports were put on heightened alert late Saturday after Canada received credible intelligence of a potential terrorist threat, CTV News has learned.

Sources say Transport Canada issued this warning to all Canadian airlines, airports and the Canadian Air Transport Security Authority.

"Further sharing of intelligence following the December 25th terrorist attempt on the United States has prompted the government to remind airlines and airports to continue to be vigilant and apply screening measures with consistency and vigour," the warning says.

British and U.S. intelligence are worried that another 20 terrorists who were trained in Yemen are heading to North America.

But sources say Canadian intelligence also had credible information of other terrorists planning to come to Canada.

Insiders say this potential threat -- and what to do about it -- was discussed with the prime minister and his national security ministers on Monday.

Federal authorities say the terrorists did not pose a direct threat to Canada. They were not planning to blow up a Canadian airliner, nor were they planning terrorist attacks at the Olympic Games in Vancouver and Whistler, or some other target in Canada.

The terrorists want to use Canada as a jumping-off point to get into the U.S., according to federal authorities.

Canadian airports tightened their security measures following a failed attempt to blow up a Northwest Airlines flight on Christmas Day.

Umar Farouk Abdulmutallab, a 23-year-old Nigerian, was arraigned on six charges, including the attempted use of a weapon of mass destruction. Last Friday, a judge entered a not guilty plea on his behalf.

In addition to the heightened security already in place, Transport Canada said it will install full-body scanners at major Canadian airports by the spring.