The United States condemned a militant attack in the Iranian capital of Tehran on Wednesday, the State Department spokeswoman said in a statement.

"The United States condemns the terrorist attacks in Tehran today," said Heather Nauert, the State Department spokeswoman. "The depravity of terrorism has no place in a peaceful, civilized world."

Suicide bombers and gunmen attacked the Iranian parliament and the Mausoleum of Ayatollah Khomeini in Tehran on Wednesday, killing at least 12 people in a twin assault.

The assaults were claimed by the Islamic State group, the first time it has taken responsibility for an attack in Iran.