A giant sunspot that erupted last week has been ranked as one of the largest solar flares seen in years, U.S. scientists said.

NASA said a powerful solar flare that erupted Thursday on the sun's surface has been classified as a powerful X1.9 flare. The flare triggered some disruption to radio communications, the U.S. space agency said on its Web site.

"Scientists are continuing to watch this active region as it could well produce additional solar activity as it passes across the front of the sun," NASA said.