In a statement released late Saturday the group said the assault intensified around the beginning of August and has since expanded to include attacks against affiliated sites.
Denial-of-service attacks work by overwhelming websites with requests for information. WikiLeaks has said it's been flooded with 10 gigabits per second of bogus traffic from thousands of different Internet addresses.
Josh Corman, with online content delivery company Akamai, characterized that as "a bit larger" than attacks commonly seen in the past few years.
WikiLeaks, which has angered officials in Washington with its spectacular releases of classified U.S. documents, remained inaccessible Sunday.