The tunnel beneath the English Channel that connects Britain to France is a Christmas terror target of Islamic terrorists, according to a report published Sunday.

The plot, which was first uncovered by the United States CIA and passed along to the French intelligence service on Dec. 19, is aimed at the heavy rush of holiday travel, according to the report in the Sunday Observer.

While there are currently no specific details, what is known comes from a secret report to the French government on terror threat levels.

U.S. security sources told The Observer the threat was "sky high."

Click here to read the original Observer story.

In reaction, British and French officials have continually checked the security system protecting the 31-mile tunnel. The French warn the threat level remains high. British security forces will remain on high alert throughout the holiday season.

French sources said the plan was formulated in Pakistan and is being directed from there. The terror plotters are believed to possibly be Britons of Pakistani descent, said the sources.

Officials report a higher number of Europeans are using the tunnel to head home for the holidays as fog continues to affect flights to and from Britain.

The report also mentions a possible Al Qaeda plan to attack an unidentified European country between September 2006 and April 2007, a plan orchestrated from Syria and Iran.

FOXNews.com's Michael De Dora Jr. contributed to this report.