The price of iron ore has fallen marginally overnight amid signs traders are waiting for a catalyst to send the market sharply higher or lower from current levels of about $US55 a tonne.

At the end of the latest offshore session, benchmark iron ore for immediate delivery to the port of Tianjin in China was trading at $US55.50 a tonne, down 0.2 per cent from its prior close of $US55.50 a tonne and still within sight of the six-year low of $US54.20 reached earlier this week.

The commodity has been bouncing around for several sessions as investors weigh a persistent oversupply against the prospect that the worst of the falls are behind the market given a 60 per cent slump in 15 months.

It has been five trading days since a two-session streak was recorded in either direction.

The directionless trade came as Fortescue Metals Group founder and chairman Andrew Forrest was busy dealing with a backlash from comments that the big miners should cap production.

While several in the iron ore sector have bemoaned the tactics of Vale, Rio Tinto and BHP Billiton as they ramp up production in an oversupplied market, Mr Forrest captured attention for calling for a definitive cap that could lift prices, with the competition watchdog assessing the comments due to concerns they may encourage cartel behaviour.

"I'm happy to put that challenge out there: let's cap our production right here and start acting like grown-ups," Mr Forrest said.

Such a move could lift prices back as high as $US90 a tonne, he suggested.

Fortescue chief executive Nev Power has since defended the comments, saying they were made simply to point out the risks to all parties of a market share war.

“The comments made by the chairman were highlighting the point that a last man standing fight for market share will damage shareholders of all companies and is not in the long term interests of our host nation Australia nor of our customers," he said.

"[T]hose comments were intended to draw attention to the fact that there is provision in Australia’s competition law dealing with the potential for discussions to be held by exporters.”