The assassination of Russian Ambassador to Turkey Andrei Karlov has led to increased tensions between the countries over the Syrian civil war. On Monday, a Turkish police officer gunned down the diplomat while condemning the war in Syria.

Russian President Vladimir Putin said the assassination was a “provocation aimed at rupturing ties between Russia and Turkey”, while Moscow’s Foreign Ministry referred to the incident as a “terrorist attack”. Putin said, “The only answer to the murder of the Russian ambassador to Turkey must be the intensification of the struggle against terrorism.”

In an address to his country, Turkish President Tayyip Erdogan said the attack was a bid to fracture its ties with Russia, which have been strained during the war in Syria. Erdogan said he and Putin have agreed to increased cooperation in the fight against terrorism, Reuters reported.

United Nations Secretary-General Ban Ki-moon condemned the shooting, which also left several others injured, and said there was “no justification for the targeting of diplomatic personnel and civilians.”

United States Secretary of State John Kerry said, “We stand ready to offer assistance to Russia and Turkey as they investigate this despicable attack, which was also an assault on the right of all diplomats to safely represent their nations.”

This shooting followed protests in Turkey against Russia’s role in the Syrian war. Russia-backed pro-government forces recently announced that the battle with the rebels was over after they took over east Aleppo, which was the last stronghold of the rebel fighters. Russia has faced strong criticism for alleged human rights violations in the war.

Turkey’s administration, which is against Syrian President Bashar al-Assad’s regime, has been attempting to salvage its relations with Moscow after shooting down a Russian warplane over Syria last year.