Saudi Arabia's King Abdullah has invited Iran's President Mahmoud Ahmadinejad to the hajj, the annual Muslim pilgrimage, Iran's state-run news agency, IRNA, reported Wednesday. Iran's ambassador to Saudi Arabia, Mohammed Hosseini, said Ahmadinejad was invited as a "special guest" to the US ally, IRNA quoted him as saying. The invitation was the first time a Saudi king has officially asked an Iranian president to participate in the pilgrimage, the agency said. There was no immediate confirmation by Saudi officials of the invitation. The hajj pilgrimage to Mecca in Saudi Arabia is a once-in-a-lifetime duty for Muslims, millions of people make the trip annually. The hajj will take place next week, though many people have already started arriving in Mecca.