From their Last.fm profile:
Mahsa and Marjan Vahdat are sisters from Iran, known primarily for vocals but also for performing the daf, a Middle Eastern drum. The pair contributed to the album “Lullabies from the Axis of Evil” (2004). Their first CD, “Songs from a Persian Garden,” was released in the United States in 2008.
View a longer version of the above performance here.
The Dish 