A woman wearing a headband that reads: 'No to an alliance of crusaders, let the Pope not come!' attends Sunday's rally in Istanbul. ((Murad Sezer/Associated Press))

Pope Benedict XVI's upcoming visit to Turkey sparked fierce protests on Sunday as more than 25,000 people gathered in one of Istanbul's major squares to demand the pontiff stay away.

There are deep concerns for the Pope's safety when he begins his visit to the predominantly Muslim country on Tuesday with the purpose to open a dialogue with the Muslim faith and the country's Christian Orthodox religion.

Protesters angered by the Pope's comments in September linking Islam to violence shouted "God is great" in Arabic and carried posters asking Benedict not to come.

"The Pope was disrespectful to us and he needs to apologize," one banner read.

Some 4,000 police backed by armoured vehicles and helicopters monitored closely as the crowd swelled in the square, which was assigned by authorities for the protest.

The CBC's Adrienne Arsenault reported Sunday's protest brought out a mixture of staunch secularists and Islamic groups. The groups rarely agree on matters of politics and religion, but appeared united in their belief that the Pope has insulted Turks and Muslims.

Visit to Blue Mosque

At the Vatican on Sunday, a spokesman confirmed the Pope would visit Istanbul's Blue Mosque as "a sign of respect" to Muslims. It will be his first visit to a mosque as Pope.

Benedict is scheduled to stay for four days in Turkey, his first official visit to a Muslim country. He will meet Turkey's president and deputy premier, as well as Ecumenical Patriarch Bartholomew I, a leader in the Orthodox Church.

The Pope outraged many Muslims in September with a speech quoting a Byzantine emperor who characterized some of the Prophet Muhammad's teachings as "evil and inhuman," particularly "his command to spread by the sword the faith."

Benedict has expressed regret for offending Muslims and said his remarks did not reflect his personal views. On Sunday, he expressed his "feelings of esteem and of sincere friendship" for Turks and their leaders.

'I don't want him in our country'

"Why is he coming?" one man in Samsun, a city on Turkey's Black Sea coast, told the CBC on Sunday. "What is the purpose of his visit, because he must know he is not welcome here."

"In Turkish we having a saying he exceeded the limits of his tongue. I believe you have to cut that tongue from its root. As Muslims, we never insult another religion, their prophet, their churches, so how dare he attack us like that? I don't want him in our country."

The Istanbul protest was organized by a pro-Islamic opposition party Felicity whose leaders have said they were offended by Benedict's comments.

Seafetin Tuleg, 70, wrapped himself in a Felicity Party flag and said Muslims revered the Jewish and Christian prophets, but did not receive the same respect for their own.

"We love Moses, Jesus and Muhammad, but the Pope doesn't love Muhammad and Islam," he said.

Kubra Yigitoglu, 20, a protester in a headscarf, ankle-length coat and cowboy boots, called Turkey an Islamic republic and said the Pope "is not wanted here."

Officially, Turkey is a rigidly secular republic, though around 99 per cent of its population is Muslim.

With files from the Associated Press