Interesting. AFP is reporting (via Iran's deputy police chief) it as a suicide bomber.
One wounded in suicide attack at Khomeini mausoleum
"A suicide bomber blew himself up at the Tehran mausoleum of Iranian revolutionary leader Ayatollah Ruhollah Khomeini on Saturday, killing himself and wounding a pilgrim, a police official told the Mehr news agency.
"Minutes ago, a terrorist detonated his explosive vest in the Imam Khomeini shrine. The blast caused damage in one section of the shrine," said Iran's deputy police chief for operations, Hossein Sajedinia.
"The bomber was killed and one pilgrim wounded," he added."