The news came as commodity prices took their biggest tumble in five months, sending investors piling out of mining and energy stocks.
And it coincided with comments from Chinalco chairman Xiao Yaqing leaving open the possibility of the Chinese aluminium giant selling its 9 per cent stake in Rio (rio.ASX:Quote,News) under BHP's (bhp.ASX:Quote,News) current offer.
The European Commission has put its review on hold while it awaits further information requested from BHP, meaning its final decision is likely to be pushed out from December 9 to some time around Christmas.
The unexpected development has fuelled concerns the regulatory body will strike down BHP's bid, as it has already expressed "serious concerns'' about the competition issues raised by the proposed mega-merger.
The Australian Competition and Consumer Commission and the international steel industry have also taken issue with the deal on the grounds that a combined BHP-Rio would wield too much control over iron ore prices.
But many commentators - not to mention the BHP camp itself - argue it is not unusual for the European competition body to ask for further information, especially when dealing with large takeover attempts.
"Suspensions are a normal part of phase two investigations under the European Commission merger regulations,'' BHP spokeswoman Samantha Evans said.
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BHP expects Rio clearance by year-end
