The Turkish, Russian and Syrian governments have condemned “the terrorist and cowardly” assassination of the Russian ambassador to Turkey, which is widely understood to be an attempt to disrupt relations between the two nations ahead of planned talks on the future of Syria.

Russian Ambassador Andrei Karlov was shot by a member of the Turkish police on Monday, a day before the meeting of foreign and defence ministers of Russia, Turkey and Iran in Moscow, and a week before planned Syria peace negotiations in Astana, the Kazakh capital.

“Don’t forget Syria! Don’t forget Aleppo!” the gunman cried before he was apprehended and shot by police.

The diplomatic channel between Russia, a longtime ally of Syrian President Bashar al-Assad, and Turkey, which backs various rebel groups, is one of the most important in the complex conflict; after years of strained relations it was Russian and Turkish diplomats who managed to broker an agreement to end the fighting in the embattled city of Aleppo last week.

The anticipated talks are seen as some of the most hopeful for ending the violence that has brutalised Syria over almost six years of war. Many in the diplomatic community are beginning to entertain the possibility of a rebel surrender now that the main groups have been pushed out of the country’s cities following the loss of Aleppo, their last urban stronghold.

The Russian and Turkish leadership, however, have presented a united front following the attack, announcing a joint investigation into the incident and emphasising that ties between the two countries should be strengthened in light of Monday’s events.

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Leonid Slutsky, the head of the foreign affairs committee in the lower house of the Russian parliament, added that Russia’s enemies “are making desperate attempts to spoil ties between Russia and Turkey, but those attempts will fail,” while Russian leader Vladimir Putin called the attack a “provocation.”

Mr Putin and Turkish President Tayyip Erdogan spoke on the phone on Monday night. Mr Erdogan said the leaders agreed the attack was “wrecking the normalisation of Russian-Turkish relations and the Syrian peace process.“

Mr Putin ordered security at Russian embassies around the world to be stepped up, adding that he wanted to know who had “directed” the gunman's hand.

In a televised statement, Turkish Prime Minister Binali Yildirim stressed that the Turkish government will also not allow Mr Karlov’s assassination to harm Russian-Turkish relations.