Wheat at 23-month high on Russia curbs

US wheat futures jumped more than 5 percent on Friday, taking weekly gains to around 25 per cent as Russia's move to temporarily halt grain shipments sparked a buying frenzy.

Chicago Board of Trade (CBOT) front-month wheat futures have nearly doubled since prices bottomed on June 9 at $4.25- per bushel as the worst drought on record in Russia, the world's third-largest exporter, destroyed crops.

Russian Prime Minister Vladimir Putin signed an order banning grain and flour exports from August 15 to December 31, with a spokesman saying this would apply to contracts that had been already signed. The news confirmed an earlier report from Interfax that kicked off the buying, according to Reuters.

CBOT wheat for September delivery surged 5.15 percent to $8.26- per tonne by 12:10 EDT, heading for its daily limit of a 90-cent rise, and striking a fresh 23-month high. The front month contract is heading for a 25 percent gain for the week.

CBOT sets daily limits to reduce market volatility with a 60-cent limit being hit on Thursday for the first time in two years after Russia said it would temporarily halt grain shipments.

"Speculation is adding fuel to the fundamentals so prices could hit a new upper daily limit," said Benson Wong, a senior advisor at Commodity Broking Services in Sydney. "It is not an investment market -- it is a speculators' market."