Istanbul, Turkey ? Tens of thousands of protesters denounced Pope Benedict XVI as an enemy of Islam at a rally Sunday that underlined deep divisions straining Turkey ahead of the pontiff’s visit this week.

Officials hoping to promote closer ties with the West urged calm, but Islamic groups wary of Western ways are united in anger over a speech Benedict gave two months ago in which he quoted a medieval text that linked Islam to violence.

Chants of “No to the pope!” rose among nearly 25,000 demonstrators at every mention of his remarks on violence and the Prophet Muhammad. Many protesters wore headbands with anti-pope slogans and waved placards that included a depiction of Benedict as the grim reaper.

The protest, organized by an Islamist political party, was the largest mass gathering so far against Benedict’s four-day visit scheduled to begin Tuesday – his first papal journey to a mostly Muslim nation. The outcry also was designed to rattle Turkey’s establishment.

Turkish officials hope to use the visit to promote their ambitions of becoming the first Muslim nation in the European Union and showcase Turkey’s secular political system. But Islamic groups, which have been gaining strength, see Benedict as a symbol of Western intolerance and injustices against Muslims.

“The pope is not wanted here,” said Kubra Yigitoglu, a 20-year-old protester wearing a head scarf, ankle-length coat and cowboy boots.

Nearby, a large banner was raised amid a sea of red flags of the Saadet, or Felicity, party. It called the Vatican “a source of terror.”

Security forces are on full alert for the pope’s visit. Nearly 4,000 police, including units in full riot guard, watched over the protest. Surveillance helicopters buzzed overhead and protesters were frisked before entering the square in a conservative stronghold of Istanbul.

The pope’s visit has two distinct – and difficult – objectives: calming Muslim ire and advancing efforts to heal a nearly 1,000-year divide in Christianity between the Vatican and Orthodox churches.

Benedict plans to meet first with political and Muslim religious leaders in the capital, Ankara, including Turkey’s president and the Islamic cleric who oversees the country’s religious affairs. Prime Minister Recep Tayyip Erdogan is scheduled to attend a NATO meeting in Latvia during the papal visit, but could briefly greet the pontiff at the airport.

The pope then heads to Istanbul – the ancient Byzantine capital of Constantinople – to be hosted by the spiritual leader of the world’s Orthodox Christians, Ecumenical Patriarch Bartholomew I.

The pope backs efforts for closer bonds between the two ancient branches of Christianity, which formally split in the 11th century over disputes including papal primacy.