Ahmed Abdullah, a Salahuddin government official who survived the blast, said: "There was a big explosion. The tent was filled with the body parts of mourners. No one can be identified."
It was the third bombing in Sunni areas in as many days.
On Sunday, a teenager killed six people in a suicide bombing in Falluja.
Police on Monday detained a number of people in Anbar province after fears that the bomber had infiltrated the so-called Awakening Council, a group of tribal leaders who have joined with US forces against al-Qaeda in Iraq.
Anbar province has been relatively calm in recent months and the US military has credited the Awakening Councils with the decline in violence.
But the military has acknowledged that it is concerned that some members could retain allegiances to al-Qaeda, particularly if they were former fighters themselves.
Rear Admiral Gregory Smith, a US military spokesman, said on Sunday that members were carefully screened and must pledge to renounce violence before being accepted.
"That's not to say that al-Qaeda has not found a way to infiltrate some members, some groups, that clearly could be the case," Smith said.