BRUSSELS, June 24 (Reuters) - European Union leaders on Thursday (Jun 23) granted Ukraine the coveted status of official candidate to join their 27-nation club, a bold geopolitical step hailed by Kyiv and the EU itself as a "historic moment".

Although it could take Ukraine more than a decade to eventually join the bloc, the decision to officially accept it as a candidate is a symbol of the EU's intention to reach deep into the former Soviet Union.

"The Ukrainian people belong to the European family. Ukraine's future is with the EU," the bloc's foreign policy chief Josep Borrell said. "Today marks the beginning of a long journey that we will walk together."

Russia's invasion of Ukraine prompted Kyiv to formally apply for candidate status, and the EU to fast-track its approval.

"Ukraine's future is in the EU," Ukrainian President Volodymyr Zelenskyy tweeted, welcoming the EU's decision as "a unique and historic moment".

Six years to the day after Britons voted to leave the EU, Ukraine's neighbour Moldova was also granted candidate status and Georgia, another ex-Soviet state, was told it would get the same once it has fulfilled more conditions.

EU leaders stressed these countries will have much "homework" to do, and after kick-starting its most ambitious expansion since Eastern European states joined after the Cold War, the bloc may need to change how it works in order to cope.

"I am convinced that they (Ukraine and Moldova) will move as swiftly as possible and work as hard as possible to implement the necessary reforms," EU Commission chief Ursula von der Leyen told a news conference.

The EU's green light "is a signal to Moscow that Ukraine, and also other countries from the former Soviet Union, cannot belong to the Russian spheres of influence," Ukraine's EU ambassador, Chentsov Vsevolod, told Reuters earlier on Thursday.

Russian President Vladimir Putin says his "special military operation" launched in Ukraine in late February was partly necessitated by Western encroachment into what Russia characterises as its rightful geographical sphere of influence.