Bomb explodes at gathering of Shiite Muslims in Pakistan; 15 reported dead

Re: Bomb explodes at gathering of Shiite Muslims in Pakistan; 15 reported dead

Can someone please calriy something for me?

The news I am hearing suggests this was a Sufi (whatever that means) gathering, and as such there were shias, sunnis an other sects at the same place?

So, was the attack against shia/sunnis or Muslims in general?