Italian police have arrested five people connected to Anis Amri, the Tunisian who carried out the 2016 Berlin Christmas market truck attack and was later killed in a shootout with police in Italy.

In a statement on Thursday, police said one of the five was believed to have procured the fake Italian identity papers that allowed Amri, a failed asylum seeker, to move around Europe.

Amri killed 12 people when he hijacked a truck and drove it into a crowded Berlin Christmas market on 19 December 2016.

The attack was later claimed by Isis. Using fake documents, he fled to Italy and died in a shootout with police near Milan four days later.

"A vast anti-terrorism operation" was being carried out by special investigation forces based in Rome and the nearby town of Latina, police said in a statement on Thursday.

The arrests were the latest in a marked uptick in recent police operations targeting suspected extremists.

Police identified the five as a Palestinian and four Tunisians and said one of the Tunisians, Akram Baazaoui, obtained the false documents for Amri.

Sources told Reuters there was no evidence the suspects participated directly in the Berlin attack or that they were preparing any imminent attack in Italy.

Berlin Christmas market lorry attack Show all 18 1 /18 Berlin Christmas market lorry attack Berlin Christmas market lorry attack Several people have been killed after a lorry drove into crowds at a Christmas market in Berlin REUTERS/Fabrizio Bensch Berlin Christmas market lorry attack 'At least nine' people have been killed and more than 50 injured. AP Berlin Christmas market lorry attack Emergency Services rush a Berlin market victim to an ambulance Associated Press Berlin Christmas market lorry attack Police cordoned off the square at Kaiser Wilhelm Memorial Church following the incident REUTERS Berlin Christmas market lorry attack Rescue workers inspect the lorry that crashed into a Christmas market close to the Kaiser Wilhelm memorial church in Berlin EPA Berlin Christmas market lorry attack Emergency crews inspect the lorry that ploughed into a Berlin Christmas market, killing at least nine people AFP Berlin Christmas market lorry attack Fire crews attend the scene of the attack AFP/Getty Berlin Christmas market lorry attack Armed police secure the site of a lorry attack at a Christmas market in Berlin REUTERS Berlin Christmas market lorry attack Crushed debris is visible beneath the wheels of the vehicle REUTERS Berlin Christmas market lorry attack An injured man is pushed to an ambulance REUTERS Berlin Christmas market lorry attack Medics attend an injured person after the lorry attack which killed at least nine and injured more than 50 people AFP/Getty Berlin Christmas market lorry attack Firefighters examine the lorry which was rammed into a Berlin Christmas market REUTERS Berlin Christmas market lorry attack A person is carried into an ambulance REUTERS Berlin Christmas market lorry attack View of the lorry that crashed into a Christmas market in Berlin, killing at least nine and injuring at least 50 people AFP/Getty Berlin Christmas market lorry attack Rescue workers push a person on a stretcher to an ambulance Getty Berlin Christmas market lorry attack Firefighters assess the damage after the lorry rammed the Christmas market, killing 'at least nine', and injuring more than 50 people AP Berlin Christmas market lorry attack Firefighters stand beside a toppled Christmas tree at the site of the suspected terrorist attack in a Berlin Christmas market AP Berlin Christmas market lorry attack Damaged stalls at the scene of the incident at a Berlin Christmas market where at least nine people have been killed EPA

As part of their operation, police were carrying out searches in Rome, the southern port city of Naples and the central and southern towns of Latina, Viterbo, Caserta and Matera, the sources said.

On Wednesday anti-terrorism police arrested an Italian citizen of Moroccan origin who they said was an Isis sympathiser planning a truck attack.

nterior Minister Marco Minniti said the security threat to Italy from Isis supporters was higher than ever because more foreign fighters were attempting to return to Europe via Italy after the jihadist group suffered defeats in Syria and Iraq.

So far this year, 29 foreigners, mostly Muslims, have been expelled from Italy as suspected threats to national security.