Crowds began converging in central Istanbul Sunday for a demonstration called by a small Islamist party against the visit to Turkey by Pope Benedict XVI, which starts on Tuesday.
The demonstration, entitled "The pope is not welcome", was scheduled to begin at 1000 GMT, but only about 600 people were in place shortly before time. However thousands more were advancing toward the square in the Caglayan district on the city's European side, slowed down at police checkpoints.
The protest organisers, the Felicity Party (SP), which is not represented in parliament, predicted a turnout of one million, but other estimates were much lower, generally at or below the 300,000 mark.
Hundreds of security forces, including riot police, were on watch.
"We have infinite respect for all religions and their representatives, but we cannot remain silent in the face of declarations that go against our faith," Osman Yumakogullari, a senior SP official, said before of the demonstration.
"In September, Pope Benedict XVI insulted the Prophet Mohammed who, according to him, brought inhumane and satanic things to the world," he said.
Yumakogullari said the pontiff failed to apologise for his controversial remarks, which triggered outrage across the Muslim world.
The SP, which hired 2000 buses to bring people to the demonstration, had modified the rally's title from "The sly and ignorant pope is not welcome," reportedly after the authorities warned them to avoid offensive slogans.
Some of the banners brandished by the crowd read: "No to the crusader's alliance."
Many Islamists and nationalists here believe the pope's scheduled talks with Patriarch Bartholomew I, the Istanbul-based spiritual head of the world's Orthodox Christians, is aimed not only at healing the centuries-old schism between the two churches, but at sealing a Christain alliance against Islam.
Under photographs of Iraq war victims, one banner asked: "Who did this?"
Another read: "Who is responsible for terrorism: the USA, Israel and the EU, or Iraq and the Palestinians?"
In anticipation of the demonstration, the pro-SP daily Milli Gazete headlined its front page Sunday with the words: "This is Istanbul, not Constantinople."
"The Pope will see in Caglayan that you cannot blot the sun out with mud," the paper wrote.
On Wednesday, police detained 39 nationalist Islamist militants at a wildcat demonstration at Hagia Sophia, a sixth century Byzantine church which is now a museum, chanting slogans against the leader of the Roman Catholic Church and holding evening prayers to stress the Istanbul landmark's five centuries as a mosque under Ottoman rule.
Nationalists and Islamists are angered at Hagia Sophia's inclusion on the pope's itinerary here on Thursday and say his visit there indicates Christian ambitions to reclaim it as a church.
The SP is an offshoot of the Welfare Party, ousted from power in 1997 and outlawed the following year for threatening Turkey's secular system.
The party's moderate members, among them Prime Minister Recep Tayyip Erdogan, left the movement and now form the core of the ruling Justice and Development Party, which has disowned its Islamist roots and describes itself as a "conservative democratic" movement respectful of secularism.