The Department of Homeland Security announced terror attacks against the United States are on the rise.

According to reports, an unclassified intelligence memo claims, "the number and pace of attempted attacks against the United States over the past nine months have surpassed the number of attempts during any other previous one-year period."

In addition, the memo warned terror organizations will target the U.S. with "increased frequency."

CNN obtained the document -- dated May 21 -- which appeared to be created for law enforcement groups throughout the country.

"We have to operate under the premise that other operatives are in the country and could advance plotting with little or no warning," it said.

The memo includes the latest attacks on New York City, including the foiled Times Square bombing attack and Najibullah Zazi's alleged scheme to blow up the city's subway systems.

Officials reportedly state future attacks will be harder to stop and warn terrorists would likely spend less time overseas "compared to lengthier training cycles for earlier operations, reducing our ability to detect their activities."

In addition, suspected terrorists will likely aim to hit ""smaller, more achievable attacks against easily accessible targets" then going for big, high-profile targets