Rewrites, adds details on deal rejection in paragraphs 2 and 4, shares in paragraph 6 and Citi comments in paragraphs 8 and 9

By Adwitiya Srivastava and Nikita Maria Jino

May 13 (Reuters) - Australia's Abacus Storage King ASK.AX has rejected an A$1.93 billion ($1.23 billion) buyout offer from a consortium led by South African billionaire Nathan Kirsh, citing risks around valuation, timing and deal completion, it said on Tuesday.

The consortium, which includes Kirsh's family office Ki Corporation and Public Storage PSA.N, offered A$1.47 per share, which was deemed insufficient by Abacus after an independent valuation pegged its net tangible assets at A$1.73 per share.

Kirsh, who has a net worth of $7.4 billion according to Forbes, already controls around 60% of Abacus Storage King with the stake being held both directly and indirectly through the billionaire's interest in the Abacus Group.

The buyout proposal also included tax-related conditions that Abacus said could add uncertainty to the deal's completion timeline.

"The acquisition price and terms offered are insufficient to compensate for this risk," the Australian company said in a statement.

Its shares rose as much as 3% to A$1.545, their largest single-day gain since April 7.

Self-storage operator and Abacus rival National Storage REIT NSR.AX bought a nearly 4.8% stake in the company in late April.

Analysts at Citi expect the Kirsh-led consortium to potentially lift its offer to more acceptable values for existing shareholders, the company, Abacus Group and National Storage.

National Storage would be more receptive of an offer at or above net tangible assets and "potentially interested in an opportunity to play a role in a revised or restructured offer," Citi analysts said.

Shares of National Storage rose 0.6% to A$2.36.

($1 = 1.5686 Australian dollars)

(Reporting by Adwitiya Srivastava and Nikita Maria Jino in Bengaluru; Editing by Rashmi Aich and Mrigank Dhaniwala)

((Adwitiya.Srivastava@thomsonreuters.com;))