Airlines across the world cancel flights

International airlines scrambled to divert or cancel flights to the United States on Tuesday following a wave of airborne terror attacks on New York and Washington.

The cancelations and diversions caused widespread confusion and congestion

at many European airports, where airlines ordered flights bound for the United States to do U-turns or find alternative landing points outside America.

German authorities ordered all U.S.-bound flights by Lufthansa canceled. A

Finnair flight out of Helsinki turned around and returned to Finland. In Belgium, Sabena Air spokesman Wilfried Remans said two flights en route to the United States were "turning around in mid-flight and returning to Brussels."

In Spain, national carrier Iberia said four scheduled flights from Madrid to the United States were in the air and three of them -- destined to New York, Chicago and Miami -- were ordered to return to Spain. The fourth, flying from Barcelona to New York, was awaiting clearance into a Canadian airport, an Iberia official said.

Scandinavian Airlines System ordered three flights bound for New York, and

another flight bound for Washington, to divert while over the Atlantic. They were expected to land instead in Iceland. SAS spokesman Thomas Brinch in Copenhagen said he wasn't sure when flights to the United States would resume.

At Heathrow Airport outside London, several flights already bound for the United States were expected to divert to Canadian airports while those that hadn't taken off were ordered delayed indefinitely.

British Airways said its U.S.-bound flights would divert to the nearest airport, or return to London.

All Canadian airports were shut down indefinitely Tuesday morning, with all domestic and international flights grounded, in the aftermath of confusion over terrorist attacks in New York City and Washington, said a senior government source in Ottawa.

Airports were accepting U.S. flights already in the air following the bombing that needed to be diverted to airports outside the U.S.

The shutdown was confirmed by a spokesman for the Calgary Airport Authority.

"All Canadian airspace has been closed other than for inbound overseas flights," said Mike Cunnington.

Airports were scrambling to find extra staff to provide information to thousands of passengers stranded as a result of the cancellations.