Fighters scrambled near Obama plane

"Two F-15 fighters from the 142nd Fighter Wing from the Oregon Air National Guard under the direction of North American Aerospace Defence Command scrambled in response to a Temporary Flight Restriction violation in the vicinity of Seattle, Washington yesterday at approximately 1:38 pm PDT," NORAD said in a statement.

"The aircraft departed the restricted airspace and was not intercepted by the fighters. A sonic boom that may have been associated with the fighters was reported to have been heard in the Seattle area," the command added in a statement.

NBC television said the intruder was a tour plane. A local television station said it had cleared the area by the time the fighters arrived, and then landed without incident.

Air space over Seattle was partly closed because of Obama's visit to the city as part of a cross-country tour.

NORAD is the binational Canadian and US command responsible for the air defense of North America and maritime warning.