The pontiff heads for more familiar religious ground on Wednesday, flying to Ephesus, western Turkey, to say mass at the location where the Virgin Mary is believed to have spent her last days.

He goes to Istanbul the same night to meet Patriarch Bartholomew I, head of the Greek Orthodox Church, for the first of a series of encounters the two men will have over the next two days.

Benedict XVI's stay in Istanbul has also been a source of controversy in nationalist and islamist circles, who accuse him of trying to forge an anti-Muslim alliance with the Greek Orthodox Church.

They are also furious at the pope's plan to tour Hagia Sophia, a 6th century Byzantine church converted to a mosque in 1453 when the Ottomans conquered Istanbul, then transformed into a museum in 1935.

Islamists, who want Hagia Sophia to become a mosque again, say the pope's visit is an indication of Christian ambitions to reclaim the Istanbul landmark as a church.

With tensions running high, security measures are extraordinary.

Foreign Minister Abdullah Gul said over the weekend that they would be even tighter than those taken for US President George W. Bush during a 2004 NATO summit in Istanbul.

1

2