 There were fears of an attack by a hijacked plane |
Italy has extended security measures which prevent private planes entering airspace over the capital, Rome. An Italian air traffic official said the ban on non-scheduled flights would continue until 6 January.
An initial six-day private flight ban was imposed on 24 December, after fears of a Christmas Day attack on the Vatican by a hijacked aircraft.
The United States has imposed temporary restrictions over key parts of Las Vegas, New York and Chicago.
Security on the ground has also been tightened in Italy.
Interior Minister Giuseppe Pisanu said earlier this month that 12,000 police and 4,000 soldiers had been deployed throughout the country to patrol some 8,000 possible targets.
In Germany, police are on high alert after a warning that Islamic militants are planning to attack a military hospital in the city of Hamburg.
The city's police said they had received a tip suggesting that extremists were planning a suicide car bomb attack.
One-Minute World News 
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