NEW DELHI: Russian President Vladimir Putin issued a statement on Monday evening condemning the fatal attack on Russia's ambassador to Turkey, Andrey Karlov, who was killed by a gunman earlier the same day in Ankara.

"This murder is clearly a provocation aimed at undermining the improvement and normalization of Russian-Turkish relations, as well as undermining the peace process in Syria promoted by Russia, Turkey, Iran and other countries interested in settling the conflict in Syria," Putin said. The "only response" to the attack that Moscow "should offer" is "stepping up the fight against terrorism," the Russian president added. "The killers will feel it.”

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Turkish officials were quick to condemn the attack. Anadolu news agency cited President Recep Tayyip Erdogan saying “I believe this is an attack on Turkey, the Turkish state and the Turkish people, and also a clear provocation to Turkish-Russian relations. I am sure our Russian friends also see this fact.”

"All the security measures around the Russian embassy and consulate general have been tightened as we agreed with Mr. Putin," Erdogan said. "Our relations with Russia are significant … I am calling on those who aim to destroy our relations: You are waiting in vain. You will never reach your goals,” Anadolu agency quoted the Turkish leader are saying.

Ambassador Karlov was gunned down on Monday by a 22-year-old Turkish police officer while delivering a speech at a cultural event sponsored by the Russian embassy in Ankara. The gunman was killed by Turkish security forces shortly afterwards. In video footage, Karlov is seen making a speech when gunshots ring out; the ambassador quickly falls to the ground. Eight bullets are said to have been fired.

The camera pulls back to show a neatly dressed gunman, wearing a suit and tie, waving a pistol. He can be heard shouting, “don't forget about Aleppo, don't forget about Syria” in Turkish.

World leaders have condemned the attack. UN Secretary-General Ban Ki-moon said he was appalled by "this senseless act of terror". The US, UK, Germany and other countries all issued statements condemning the attack. India’s Ministry of External Affairs released a statement condemning the “tragic assassination of the Ambassador of the Russian Federation to Turkey,” calling it a “dastardly act,” and adding that “there can never be any justification for violence and terrorism.”

Several hours after the ambassador was killed, a man was arrested elsewhere in Ankara for firing a pump-action shotgun in front of the US embassy. No one was hurt, but US missions in Ankara, Istanbul and Adana will remain closed on Tuesday.

Meanwhile, Moscow has said that it will be sending investigators to Turkey, and a meeting of the Russian, Turkish and Iranian foreign ministers will take place on Tuesday in Moscow.

The violence comes as Aleppo dominated the headlines in the last week, as Syrian troops backed by Russian forces moved to retake control of the city from rebel groups. A contentious ceasefire was finally implemented to safeguard civilian lives, and on a political level, Turkish and Russian governments have been co-operating in the ceasefire operation.

Tensions between the two countries, however, have been high as world powers stand divided over the future of Syria, with the Russians backing Syrian President Bashar al-Assad, and Turkey being part of the US-led coalition that is aiding rebel groups in the fight against Assad.

These tensions were particularly heightened last year, after a Turkish plane shot down a Russian jet close to the Syrian border. In fact, the shooting down of the Russian jet by Turkish forces was the first diplomatic crisis ambassador Karlov had to deal with.

Meanwhile, in other international news, German police are investigating a "probable terrorist attack" after a man ploughed a lorry into a Christmas market in Berlin, killing 12 people and injuring 48. The driver has been detained, with news reports suggesting that he is an Afghan or Pakistani asylum seeker.