Pope Benedict yesterday embarked on a second mission in Turkey, to improve ties between Catholic and Orthodox Christians, after winning praise for his conciliatory views on Islam and the country's future in Europe.

Pope Benedict and Ecumenical Patriarch Bartholomew, the spiritual head of the world's 250 million Orthodox, both want to take steps to heal the split dating from the Great Schism of 1054.

In a gesture showing their close ties, Patriarch Bartholomew took the unusual step of welcoming the Pope at Istanbul airport as he arrived from saying mass in Ephesus in southwestern Turkey.

Pope Benedict, who earlier yesterday visited a house near Ephesus said to be where the Virgin Mary died, won widespread praise in local media for backing Ankara's bid to join the EU and saying Islam was a peaceful faith.

The Iraqi wing of al Qaeda was not pleased, however. It said on a website his visit was part of a crusade against Islam aimed at pulling Turkey out of the Muslim world and into "the quagmire of secularism".

The Vatican spokesman said neither the Pope nor his entourage are worried but that al Qaeda's message confirmed the urgent need for a common commitment against the use of violence.

At a solemn service at the Orthodox Patriarchate, Pope Benedict and Patriarch Bartholomew lit candles and exchanged words of welcome amid ringing church bells as police sharpshooters stood on roofs and helicopters flew overhead in a massive security operation.

Security was so tight that an armoured personal carrier trailed the papal motorcade from the airport to the centre of Istanbul, known as Constantinople when it was the capital of the Byzantine Empire.

The leader of 1.1 billion Roman Catholics must walk a fine line to avoid upsetting the Turks, some of whom suspect Patriarch Bartholomew - who is a Greek Orthodox - of being a tool of their old rival Greece.

Some Turkish commentators debated whether the Pope was in Turkey to strengthen the influence of Christians at the expense of the country's secularist system.