Vladimir Putin has ordered his secret services to tighten security for Russians at home and abroad.

The move comes a day after Russia’s ambassador to Turkey Andrey Karlov was shot dead by a Turkish off-duty policeman while speaking at an art gallery.

Russian news wires quoted Mr Putin as saying: I ask the special services to take additional measures to ensure security inside Russia and outside, to raise the security of Russian institutions and employees abroad.

And I ask you through channels of partnerships to strengthen your work with the intelligence agencies of other states.

Moscow has already described the killing of Mr Karlov by gunman Mevlut Mert Altintas as a terrorist act.

Mr Putin’s spokesman, Dmitry Peskov, said 18 Russian investigators and foreign ministry officials had flown to the Turkish capital.

Among their priorities will be trying to determine whether Altintas was a lone gunman or operating as part of a wider plot, Hurriyet newspaper reported.

Meanwhile, Mr Karlov’s body has now been returned to Russia after an official farewell ceremony at Ankara’s Esenboga airport.

:: The outlook for Russia-Turkey ties after the ambassador’s death

Russian foreign minister Sergei Lavrov said Mr Putin and Turkish president Recep Tayyip Erdogan had agreed the killing of Mr Karlov makes us more decisive in fighting terrorism and makes today’s meeting even more important.

Turkey’s state-run Anadolu news agency said six people had been detained in connection with the assassination.   

Anadolu said Altintas’ mother, father, sister and two other relatives had been held in the western province of Aydin.

Police also detained his flatmate in Ankara.

(c) Sky News 2016: Russia tightens security after shooting of Turkish ambassador