Passengers sleep at Edinburgh Airport, in Scotland May 24, 2011. Ash from an Icelandic volcano forced the cancellation of dozens of flights to and from Scotland on Tuesday but Ireland's Ryanair said it would protest against "unnecessary" restrictions. [Photo/Agencies]

BRUSSELS - The European air traffic agency says up to 500 commercial flights in Northern Ireland, Scotland and parts of Scandinavia may be canceled Tuesday because of the spread of volcanic ash.

Related readings:  Volcano ash halts air traffic, could reach Denmark

Brian Flynn, head of network operations at Eurocontrol, said Tuesday morning that between 200 and 250 flights had already been canceled.

There are just over 30,000 flights within Europe on average every day at this time of the year.

Flynn said he did not expect that President Barack Obama's European tour would be affected by the ash.

"I think he will be able to continue his visit to Europe as scheduled," Flynn said. The ash already forced Obama to shorten a visit to Ireland.