In a document marked "secret" sent to members of the World Trade Organisation last week and seen by Reuters, Ukraine says it intends to raise the limit on the tariffs it can legally impose on more than 350 goods. Based on figures in the proposal, Kiev's plan would hit overall imports worth more than $4.6 billion in 2011.

The document, which diplomats said they had received on Sept. 14, consists of 85 pages of annexes detailing the items affected. It says Ukraine is prepared "to enter into negotiations and consultations" with WTO members for the concessions.

There was no response to requests for comment from Ukraine officials in Geneva or Kiev. Ukraine, a relative newcomer to the WTO whose trade deficit widened by more than 50 percent last year to $14 billion, has already threatened to block car imports and said last year it would act to improve its terms at the WTO.

The United States said Ukraine's possible decision would raise "serious concerns", although WTO officials played down the move, which, though radical, is permissible under the agency's rules.

Some trade experts fear the plan, which would force hundreds of trade deals to be renegotiated, could trigger increasingly protectionist policies worldwide. The four-year-old global financial and economic crisis has so far not led to a rush to protectionism but, under pressure to help their producers weather the storm, governments have pounced on "unfair" moves by their rivals. The United States and Brazil were the latest to trade diplomatic blows.

WTO Director General Pascal Lamy, who forecast on Friday that world trade would grow by a mere 2.5 percent this year, has repeatedly warned of the danger of a return to protectionism.