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St Peter's Basilica in Rome, along with Milan's cathedral and La Scala opera house, could be "potential targets" for future Isis attacks, the US State Department has warned.
Other targets could include "general venues" such as churches, synagogues, restaurants, theatres and hotels.
Italian law enforcement are currently "working to identify five people" identified by the FBI, according to Paolo Gentiloni, Italy's foreign minister.
The news comes as the Iraqi branch of Isis posted a video threatening fresh suicide and car-bomb attacks, titled Paris Before Rome.
They particularly mention attacks against France and the US.
"We will end with what is called the White House and we will blacken it with our fire," one militant says in the video.
In a security message to US citizens living in Italy, the US embassy said: "Terrorist groups may possibly utilise similar methods used in the recent Paris attacks."
Show all 25 1 /25The world mourns Paris attacks - in pictures The world mourns Paris attacks - in pictures The world mourns Paris attacks Members of the public gather to lay flowers and light candles at La Belle Equipe restaraunt on Rue de Charonne in Paris
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The world mourns Paris attacks - in pictures The world mourns Paris attacks People lay a memorial to honour victims of the Paris terror attacks at Federation Square in Melbourne, Australia
The world mourns Paris attacks - in pictures The world mourns Paris attacks Soccer fans display the colors of the French flag in response to the deadly terrorist attack in Paris, France before the soccer match between the New York Cosmos' and the Ottawa Fury for the North American Soccer League championship at Hofstra University in Hempstead, New York, USA
The world mourns Paris attacks - in pictures The world mourns Paris attacks Pakistani Civil society activists shout slogans during a protest against Isis militants near the French consulate for the victims of the 13 November Paris attacks in Karachi, Pakistan
The world mourns Paris attacks - in pictures The world mourns Paris attacks People gather and view messages written on the ground at Place de la Republique in Paris
The world mourns Paris attacks - in pictures The world mourns Paris attacks French flags and a note reading "We will not let you spoil our children's lives" at the site of the attack at the Cafe Belle Equipe on rue de Charonne in the 11th district, in Paris
The world mourns Paris attacks - in pictures The world mourns Paris attacks A rose is placed beside a bullet hole at La Belle Equipe restaraunt on Rue de Charonne following the terrorist attack in Paris. As France observes three days of national mourning members of the public continue to pay tribute to the victims of deadly attacks
The world mourns Paris attacks - in pictures The world mourns Paris attacks
The world mourns Paris attacks - in pictures The world mourns Paris attacks Bono and band members of U2 pay their respects and place flowers on the pavement near the scene of yesterday's Bataclan Theatre terrorist attack in Paris
The world mourns Paris attacks - in pictures The world mourns Paris attacks A man kneels as he pays tribute to victims at Place de la Republique near the deadly attack sites in Paris
The world mourns Paris attacks - in pictures The world mourns Paris attacks Tributes to the victims at the Place de la Republique square in Paris
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The world mourns Paris attacks - in pictures The world mourns Paris attacks An electronic billboard on a canal show solidarity with Paris in Milan
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The world mourns Paris attacks - in pictures The world mourns Paris attacks People lay down flowers and light candles to tribute victims of Friday's attacks in Paris as the Brandenburg gate is illuminated in blue, white and red in the colors of the French flag, in Berlin
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The world mourns Paris attacks - in pictures The world mourns Paris attacks A man leaves flowers as a tribute following the deadly attacks in Paris, outside the French consulate in Istanbul
Reuters
The world mourns Paris attacks - in pictures The world mourns Paris attacks People take pictures of flowers placed in bullet holes in the window of a Japanese restaurant next to the cafe 'La Belle Equipe'
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The world mourns Paris attacks - in pictures The world mourns Paris attacks People gather at a makeshift memorial next to the Bataclan theatre in Paris on November 14, 2015,
The world mourns Paris attacks - in pictures The world mourns Paris attacks A woman carrying flowers cries in front of the Carillon cafe and the Petit Cambodge restaurant in Paris
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The world mourns Paris attacks - in pictures The world mourns Paris attacks People gather in front of flowers that were laid outside the French embassy in Rome
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The world mourns Paris attacks - in pictures The world mourns Paris attacks People react near the cafe 'La Belle Equipe' at the Rue de Charonne
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The world mourns Paris attacks - in pictures The world mourns Paris attacks A young girl places a candle in front of the Carillon cafe in Paris
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The world mourns Paris attacks - in pictures The world mourns Paris attacks Flowers placed outside the cafe 'La Belle Equipe' at the Rue de Charonne in Paris, the scene for one of the attacks
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The world mourns Paris attacks - in pictures The world mourns Paris attacks A woman is comforted by others outside the Carillon cafe and the Petit Cambodge restaurant in Paris
The world mourns Paris attacks - in pictures The world mourns Paris attacks The Brandenbourg Gate featuring French national colors is pictured in Berlin, on November 14, 2015 a day after deadly attacks in Paris
The world mourns Paris attacks - in pictures The world mourns Paris attacks Flowers are laid in front of the French embassy in Rome
EPA
The world mourns Paris attacks - in pictures The world mourns Paris attacks A candle is lit next to flowers outside the French Embassy in Berlin
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"The Italian authorities are aware of these threats," it added.
Following last week's attacks, around 700 soldiers are being deployed in Rome for added security.
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