The group said in a message this week marking the start of Ramadan it intended to strike at the "heart" of the United States.
"You will soon witness how attacks will resound in the heart of your land, because our war with you has now started," said a man that identified himself as Abu Bakr Baghdadi, the pseudonym used by the head of the group.
This particular branch of al-Qaida, which has primarily focused on attacking U.S. forces in Iraq, as well as Iraq's Shiite-led government, has become stronger in the last year with the help of cash from wealthy benefactors and now appears to be plotting attacks on U.S. soil, the Los Angeles Times reported Thursday.
"You can say pretty categorically that al-Qaida in Iraq appears to be strengthening from where it was two years ago," Seth Jones, author of "Hunting in the Shadows: The Pursuit of al-Qaida since 9/11," was quoted as saying.
Several associates of the group have been arrested in the U.S. and Canada in the last two years, highlighting the potential threat, Matthew Olsen, the director of the National Counterterrorism Center, said Wednesday during a hearing before the House Homeland Security Committee.
U.S. Rep. Michael McCaul, R-Texas, who serves on the House committee, said there is "a heightened sense of concern for law enforcement and intelligence agencies," the Times reported.