Rebel authorities in east Ukraine have detained several suspects and declared three days of mourning after the assassination of top separatist leader Alexander Zakharchenko.
The 42-year-old head of the self-proclaimed Donetsk People's Republic was blown up at a cafe in the rebel-controlled city in broad daylight on Friday, becoming the four-year conflict's most prominent victim from the Moscow-backed side.
Zakharchenko's bodyguard was also killed and 12 more people injured, said the official website of the region.
"Several people have been already detained" as a result of an operation to find those responsible for Zakharchenko's murder, the acting head of the region Dmitry Trapeznikov told reporters late Friday.
He added that security had been strengthened and the borders shut, meaning no-one can cross into Kiev-controlled territory or neighbouring Russia.
Moscow and rebel authorities have pointed the finger at Kiev. Trapeznikov said the detained helped confirmed that the blast was "a sabotage by Ukraine".
Ukraine counters that the crime is tied to internal strife and Russia's desire to control the territory.
The rebel authorities declared the period of mourning until Monday and delayed the start of a new school year until Tuesday.
More than 10,000 people have been killed since the rebel insurgency broke out in the eastern Donetsk and Lugansk regions in April 2014 following Russia's annexation of Crimea from Ukraine.
Kiev and its Western allies accuse Russia of funnelling troops and arms across the border.
Moscow has denied the allegations despite evidence it has been involved in the fighting.
Other top figures who have been killed outside the battlefield include commanders Mikhail Tolstykh and Alexei Mozgovoy.