World on high alert as gun cops patrol Christmas markets after four atrocities leave 15 dead in ONE DAY

CITIES across the world are on high alert after four suspected terror attacks in just 24 hours, with armed police guarding Christmas markets and shopping centres.

Ankara, Berlin, and Zurich have all been targeted in a series of terrifying incidents which have claimed the lives of at least 15 people.

Brussels police also confirmed a "large security anti-terrorist operation" yesterday, with one person arrested in the Schaerbeek area of the city on suspicion of posting terrorist threats.

Firearms and a computer were seized as an explosive devices unit examined a suspicious package - but no explosives were found.

The UK is on lock-down with undercover SAS soldiers and armed cops patrolling high streets and shopping centres, with police warning an attack is "highly likely".

Eleven forces are sending out anti-terrorism police patrol squads to cities in a bid to spot and stop any ISIS or al-Qaeda inspired attacks.

Scotland Yard has vowed to review protection of Christmas and New Year events as the terror threat level remains at "severe".

London, Manchester, Birmingham and Leeds will all benefit from extra protection after MI5 warned that ISIS extremists are targeting mainland Britain as well as cities across Europe.

Paris have also stepped up security, with armed police patrolling streets and several markets restricted to pedestrians only.

Yesterday afternoon the Russian Ambassador to Turkey was assassinated in an art gallery by an off-duty cop who shouted "We die in Aleppo, you die here."

Andrei Karlov, 62, was giving a speech at an art gallery when Mevlüt Mert Altintas, 22, fired at him at least eight times.

He was rushed to hospital but succumbed to his injuries, and Altintas was killed by police in an intense shootout after incident.

No group claimed responsibility but Russia said it considered the diplomat's death an act of terror.

Hours later, the US embassy in Ankara was in lock-down after a man reportedly fired a pump-action shotgun 'eight or nine times' outside.

He was arrested after a stand-off with the police just 2.5 miles from where Andrei Karlo was gunned down.

In the same afternoon, a man entered a mosque in Zurich and opened fire on a group of worshippers. The mystery shooter seriously wounded two people and injured another before fleeing the scene.

Police were still hunting for him hours later when his body was found on the river bank nearby.

And last night 12 people were killed and 50 injured when a Pakistani refugee ploughed a hijacked truck into a Christmas market in Berlin, Germany.

The suspect, named locally as Navid B, is believed to have been recently radicalised in Germany and may have been ordered by an ISIS handler in the Middle East to carry out the attack.

The terrorist group claimed responsibility for the massacre last night, which took place in a busy market full of tourists and shoppers.

One of the victims was the original truck driver, who is believed to have been shot as the attacker took control of the vehicle.

His body was found in the cabin after the vehicle careered through Breitscheidplatz at 7pm.

It mounted the pavement before crashing into a crowd of shoppers, tearing through stalls before coming to a stop after a deadly 150ft rampage outside the Kaiser Wilhelm Memorial Church.

The latest attacks come after several others in Germany this year.

In July a German teen shot dead nine people in Munich before turning the gun on himself, just days after an Afghan refugee .

In the same month a 27-year-old Syrian due to be deported blew himself up outside a bar in Ansbach, wounding 15 people.

In May a German man allegedly shouted "Allahu Akbar", stabbed a person to death and slashed three others at a railway station in Grafing.