UPDATE 1-Russian-backed separatists in Donetsk to hold vote on joining Russia on Sept. 23-27

(Adds quote from DPR head)

Sept 20 (Reuters) - Russian-installed separatists in Ukraine's eastern Donetsk region said on Tuesday they will stage a referendum on Sept 23-27 on joining Russia, and called on President Vladimir Putin to admit their territory to Russia as soon as possible after the vote.

In a post on social media addressed to Putin, Denis Pushilin, head of the self-proclaimed Donetsk People's Republic (DPR) wrote: "I ask you, as soon as possible, in the event of a positive decision in the referendum - which we have no doubt about - to consider the DPR becoming a part of Russia."

The separatist Luhansk People's Republic (LPR) also said on Tuesday it intends to hold a referendum on joining Russia on the same dates, and Russian-installed officials in occupied parts of Kherson and Zaporizhzhia provinces have made similar calls.

Russia recognised Luhansk and Donetsk as independent countries at the start of its invasion in February, and now says securing their territory is the main purpose of its "special military operation". (Reporting by Reuters; Editing by Jon Boyle and Peter Graff)