Russia's ambassador to Turkey was shot dead when a lone gunman fired at him at a photo exhibition in Ankara, Turkey's capital.
The ambassador had been attending a photo exhibition called "Russia as seen by Turks".
Video of the event shows Mr Karlov making a speech when gunshots ring out. Eight bullets are said to have been fired.
The camera pulls back to show a smartly dressed gunman, wearing a suit and tie, waving a pistol and shouting in Arabic and Turkish.
He can be heard yelling "don't forget about Aleppo, don't forget about Syria" and uses the Arabic phrase "Allahu Akbar" (God is great).
He is said to have died in a shootout with police soon afterwards.
Mr Karlov was rushed to hospital but his death was later confirmed by the Russian foreign ministry.
The Russian president, Vladimir Putin, called the killing a “provocation” aimed at sabotaging a rapprochement between Moscow and Ankara and attempts to resolve the conflict in Syria.
Putin said: “There can be only one answer to this - stepping up the fight against terrorism, and the bandits will feel this.”
“We have to know who directed the hand of the killer,” he said.
Condemning the attack as an act of "terrorism", Russian foreign ministry spokeswoman Maria Zakharova said Turkey had given assurances that there would be a comprehensive investigation, and those responsible would be punished.
"We know that this is a provocation on destroying the relationship between Turkey and Russia during this normalization process. ... All the expectation of what they want to achieve with this attack will be in vain and never happen," Erdogan said in televised remarks Monday.
The UN Security Council strongly condemned ambassador Andrei Karlov's murder, while Secretary-General Ban Ki-moon said he was appalled by "this senseless act of terror".
A tractor trailer barreled into a crowded Christmas market in Berlin on Monday night, killing 12 people and injuring 48 others. Witnesses said shoppers screamed and dropped packages and glasses of mulled wine as the truck plowed into the market.
The stall that we bought our mulled wine from was completely crushed. People were tearing off wooden panels to get out. It was not an accident. It was going 40mph, it was in the middle of the market. There was no way that it could have come off the road and it showed no signs of slowing down.
I just saw this huge black truck speeding through the markets crushing so many people and then all the lights went out and everything was destroyed. I could hear screaming and then we all froze. There was blood and bodies everywhere.
I don't want to use the word 'attack' yet at the moment, although many things speak for it. There is a psychological effect in the whole country of the choice of words here, and we want to be very, very cautious and operate close to the actual investigation results, not with speculation.
Authorities have apprehended the suspected driver, according to a police spokesman.
The suspect was a refugee from Pakistan the media in Germany reported. While one section of the media claimed that the suspect may have come from Pakistan others said that he may have been of Afghan origin.
The original driver, who was transporting steel beams from Poland to Germany, was a Polish national who was found dead in the lorry's cabin. It is thought he was hijacked.
There have been no reports of Chinese nationals among the victims so far. The Chinese embassy in Germany issued a safety notice on Tuesday, reminding Chinese citizens in Berlin to be alert and keep all lines of communication open.
It came after repeated warnings from various security agencies that ISIS planned to wreak havoc on European countries during the festive season, specifically threatening Christmas markets.
Just weeks ago, tourists were warned by the US State Department to be on high alert if visiting traditional markets in Europe due to a heightened terror threat.
Monday's incident evoked memories of the lorry attack on Bastille Day crowds in the French city of Nice on 14 July, when 86 people were killed. That attack was claimed by so-called Islamic State (IS).
Both ISIS and al-Qaida have urged their followers to use trucks as a means to attack crowds.
基地组织曾在一篇文章中称卡车是“The Ultimate Mowing Machine”（终极割草机）。
ISIS则鼓励对付敌人就要“Run him over with your car”（用你的车碾压他）。
昨天傍晚5点半左右，瑞士最大城市苏黎世一清真寺发生枪击事件，三人受伤，凶犯仍然在逃（the suspect remains at large），动机不明。
A gunman opened fire in a Muslim prayer center in Zurich, the largest city in Switzerland, late on Monday afternoon, wounding at least three people, according to the police.
Around 5:30 p.m., the gunman entered the prayer center, in a neighborhood known as Aussersihl, just south of the city’s main train station. Several worshipers were praying.
The assailant opened fire, injuring three men, ages 30, 35 and 56, before fleeing. The men were taken to a hospital. Two of the three were injured seriously, and one was lightly wounded, the police said.
The attacker, believed to be about 30 years old, fled the scene. Both city and cantonal police began a search for the attacker and appealed for witnesses to come forward.
The police later reported that the body of a man had been found on Monday evening on the Gassner Bridge, which crosses the River Sihl in the center of Zurich. The identity of the man as well as the circumstances of his death were not immediately clear. Also unclear was whether the body had any connection to the shooting, which occurred a short distance away.
Authorities weren't considering the attack as terrorism, a police spokesman said. Police also said it was too early to determine whether there might be any link to an incident in Berlin also on Monday.
Police forces and authorities across Europe have upped their security measures this evening.
Thousands of people have been marking themselves as 'safe' on Facebook as the social media site gives people an opportunity to let their loved ones know they are out of danger.
编辑：唐晓敏 祝兴媛 左卓