Anti-Christian banners and billboards have sprung up along the main route to Nazareth’s Roman Catholic church days before Pope Benedict XVI is due to arrive in Israel’s largest Arab city to conduct an open-air mass.

The signs, including one denouncing those who “harm God or his messenger”, have been posted by a radical Islamic group in the city as part of a campaign to stop the Pope’s visit.

Nazareth officials are publicly downplaying the significance of the signs, though privately they fear they will be highly visible as the Pope passes through the main street of Nazareth accompanied by tens of thousands of pilgrims.

But the municipality is reported to be wary of removing the posters for fear of triggering protests from radical Muslims that could turn violent.

Meanwhile, Israeli police are gearing up for possible trouble and will deploy thousands of officers in Nazareth for the Pope’s arrival on Thursday and seal off sections of the city for 24 hours beforehand.

They have also requested that Pope Benedict not use his popemobile in the city, although Vatican staff are reported to have overruled them.

Muslims around the world were angered by a speech in 2006 in which the Pope quoted from a Mediaevel text that characterised the Prophet Mohammed’s teachings as evil.

He later clarified that he did not personally subscribe to the view of Islam he quoted.

In Israel the influential northern wing of the Islamic Movement has called for a “boycott” of the visit.

But a radical Islamic group in Nazareth appears to have taken opposition to the Pope further by posting the signs next to the city’s main church, the Basilica of the Annunciation, which marks the spot where Mary is believed to have been told of her immaculate conception.

Pope Benedict is scheduled to hold his only meeting with the Israeli prime minister, Benjamin Netanyahu, in the Basilica.

A public square in front of the church has been a flashpoint since the late 1990s, when an Islamic group won approval from the Israeli government to build a large mosque there, in a project that would have obscured the Basilica from public view.

Clashes between Muslims amd Christians broke out at the square in Easter 1999, shortly before Pope John Paul II visited for the millennium.

The government made a dramatic U-turn in 2003 – reportedly on orders from the Bush administration – and sent in armed police to demolish the mosque’s foundations. The radical Muslims are known locally as the Shihab a-Din group because they claim the square is a holy place. It includes a tomb to Shihab a-Din, a nephew of the Islamic warrior Saladin, who defeated the Crusaders more than 800 years ago. The group has established a makeshift mosque in the grounds of the tomb.

Sheikh Nazim Abu Saleem, the mosque’s preacher, has made a series of declarations against the Pope. He recently told The Jerusalem Post newspaper that Pope Benedict had “declared war on Islam” and that “We cannot accept whoever insults the Prophet”.

Asked about the potential for violence, he added: “We don’t have the power to control people … We can’t prevent people from expressing how they feel or the manner in which they express it.”

The Quranic messages on the signs – in Arabic and English – appear to have been selected for their shock value, especially in a city where a third of the population is Christian and sectarian relations are delicate.

One says: “And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers.”

Another warns that “those who are with him [Mohammed] are severe against disbelievers, and merciful among themselves”.

Although the core Shihab a-Din group numbers only a few dozen, hundreds of Muslims in Nazareth show support each Friday by praying in the square next to the tomb.

A regular at the Shihab a-Din site, Kamal Abu Shakra, 32, a felafel store owner, said there was widespread anger against the Pope.

“He is not welcome here and through these signs we will make sure the world knows that.”

He said he had been jailed for five days in 2003 when he stood in the way of police seeking to destroy the mosque’s foundations.

He added, however, that his group had no interest in provoking violence with Christians in the city.

Sari Ali Mohammed, who runs a ceramics giftshop with his father next to the Baslica, said there was always a danger of sectarian violence breaking out in the city. “We are living on a knife-edge.”

Ramez Jeraisi, Nazareth’s mayor, called the Islamic group “extremists who represent neither Nazareth’s Muslims nor Christians”.

He hoped the signs would be removed before the Pope’s arrival, but did not want to risk a confrontation.

“This group wants to draw us into a conflict for the publicity but we refuse to play their game.”

Nazareth is home to about 25,000 Christians and twice that number of Muslims, many of the latter refugees from neighbouring villages displaced during the 1948 war that founded Israel. The city also serves a much larger Christian population from nearby towns and villages in the Galilee.