A Republican Jewish group is demanding an apology from senior Obama campaign adviser David Axelrod after he referred to Mitt Romney's ad campaign in Illinois as "the Mittzkrieg."

"The Mittzkrieg in Illinois isn't terribly inspiring, so turnout may lag," Axelrod said via Twitter referring to the Illinois primary Tuesday. "But the sheer volume probably has been grindingly effective."

The comment appears to compare Romney's effort against GOP rival Rick Santorum with the blitzkrieg, a military strategy developed by the Nazis during World War II to bombard the Allies with ground and air forces.

Romney and his affiliated super PAC - Restore Our Future - have outspent Santorum and his affiliated super PAC - Red, White and Blue Fund - through what have been largely negative ad campaigns by eight to one, according to ABC News estimates.

The Republican Jewish Coalition condemned the comparison of Romney's effort to the blitzkrieg as casual and inappropriate use of Nazi imagery and demanded an apology.

Axelrod is himself Jewish.

"At a time when there is so much talk about the need for civility in political discourse, it is disturbing to see President Obama's top campaign adviser casually throw Nazi imagery around in reference to a Republican candidate for president,"  the group said in a statement. "Holocaust and Nazi imagery are always inappropriate in the political arena. Axelrod should apologize for his offensive language."

Romney campaign spokesman Eric Fehrnstrom circulated the RJC statement, saying the group "slaps @davidaxelrod for 'Mittzkrieg comment, saying 'Holocaust and Nazi imagery' inappropriate."

A spokesman for the Obama campaign did not immediately respond to ABC News' request for comment.

National Jewish Democratic Council president and CEO David A. Harris said, "Jewish Republicans' protest to this supposed reference is too much, methinks. Their silence has been beyond deafening when actual, direct abusive Holocaust rhetoric has been invoked by key Republicans - such as Rep. Allen West recently saying that infamous Nazi Joseph Goebbels would 'be very proud of the Democrat Party.' Their party is thick with it, from the top down. Nice try, but a real start would be addressing the widespread abusive Holocaust rhetoric that permeates the right - disturbingly employed on a regular basis."

ABC News' Elizabeth Hartfield contributed to this report.