St. Peter's Basilica tops the list of potential targets for terrorist attacks in Rome and Milan, the U.S. Embassy in Rome said Wednesday, in the wake of Islamic State militants' Nov. 13 attacks in Paris.

"Terrorist groups may possibly utilize similar methods used in the recent Paris attacks. The Italian authorities are aware of these threats," the embassy said in a Nov. 18 security message.

Other potential targets include Milan's cathedral and its opera house, La Scala. The embassy's security message also noted venues such as churches, synagogues, restaurants, theatres, and hotels in both cities.

The embassy advised U.S. citizens in Italy to be "vigilant and aware of their surroundings," and  encouraged them to monitor news media.

In the Nov. 13 attacks in Paris, three teams of terrorists killed 129 people.

A Wednesday raid by French police killed Abdelhamid Abaaoud, a Belgian citizen about 27 years old who is believed to have been the ringleader. The Morocco-born Abaaoud was linked to several terrorist plots, including an April plan to attack a church in the Paris suburb of Villejuif, the New York Times reports.

During the raid, a woman opened fire on police and then detonated a suicide vest, killing herself. She was later identified as Abaaoud's cousin. French police are seeking another suspect, and have arrested scores of suspected militants in more than 600 raids.

Last week Cardinal Pietro Parolin, the Vatican's Secretary of State, told French daily La Croix that the Paris attacks showed no one was safe.

"The Vatican could be a target because of its religious significance. We are capable of increasing the level of security in the Vatican and the surrounding area," he said in an interview published Nov. 15.

However, he added: "we will not let ourselves be paralyzed by fear."

Cardinal Parolin said that Pope Francis will not change his agenda in the wake of the attacks.

The cardinal's interview reaffirmed the need to stop unjust aggression and "blind violence." He said that ordinary Muslims must be involved in countering extremism. They too must be "part of the solution" to terrorism, he said.