DONETSK, Ukraine (REUTERS) - A pro-Russian separatist leader was sworn in on Tuesday as the head of a self-proclaimed "people's republic" in eastern Ukraine in a ceremony that worsened a standoff with Russia.

Alexander Zakharchenko, who was elected in a rogue vote on Sunday that was denounced as a "farce" by Kiev and illegitimate by the West, took the oath to "honestly serve the interests of the people of the Donetsk People's Republic and conscientiously fulfil my duties."

Before the ceremony, which took place in a drama theatre in Donetsk, a big industrial city and the separatists' stronghold, another separatist figure, Andrei Purgin, said: "We are starting a history with this inauguration and what happens today will be repeated. We are laying down the traditions of the Republic."

Kiev's pro-Western leaders fear that a new "frozen conflict"could now be created in its eastern regions and further threaten the territorial unity of Ukraine, which lost control of its Crimean peninsula in March when it was annexed by Russia.