(Adds details on demerger plan, share performance) June 22...

(Adds details on demerger plan, share performance)

June 22 (Reuters) - Australia's AMA Group (AMA) said on Friday it has halted a deal to sell its vehicle panel repair arm to Blackstone Group BX.N for A$508 million ($375 million) following an unfavourable ruling from the Australian Taxation Office.

AMA shares fell as much as 5.6 percent on the news, hitting their lowest level since April 13, when the deal was announced. It said no break fees would be payable.

AMA had also announced in April that it would separately spin off its automotive component, accessory and procurement business.

Under the Blackstone deal, shareholders were to receive A$0.86 per share for their stake in the repair business either wholly in cash or through a cash and unlisted scrip mix.

"The AMA Board is disappointed that the Deputy Commissioner of Taxation has taken a different view as to the requirements for demerger relief as compared with previous transactions," AMA said in a statement.

The company reiterated it was on target with market guidance released earlier this year. ($1 = 1.3557 Australian dollars)