U.S. markets will act with "caution and thought" to news that London has been hit by a series of bomb blasts, according to James Park, director of institutional trading at Rodman & Renshaw. "Undoubtedly this brings back the sentiment of 9/11," said Park, referring to the terrorist attacks on the World Trade Center in New York in 2001. "But I believe market participants will act with caution and thought and most importantly with sympathy to those immediately affected by this act."