The Commerce Department said it was filing motions "requesting clarification" of the October 5 decision by the panel of the North American Free Trade Agreement.

The US agency said it was also requesting an extension of time to file a response until it gets a clarification.

"This administration is fully committed to Nafta and to coming to a lasting agreement with Canada to resolve this dispute," said Commerce Secretary Carlos Gutierrez.

"The Department has requested clarification because we have significant questions about the methodology applied by the Nafta panel."

A Commerce Department official, speaking on condition of anonymity Friday, said the United States would continue to collect duties on Canadian softwood in the meantime.

"We're not trying to delay things, we're trying to do it right," the official said.

The trade row has soured relations between Ottawa and Washington, with Canadian officials breaking off talks to protest a US decision to continue to collect duties on Canadian softwood imports despite the Nafta ruling.

The panel established under Nafta had previously ruled that Canadian imports of softwood lumber had not harmed the US lumber industry.

Canada is seeking a refund of the estimated four billion US dollars in duties on Canadian softwood imports since May 2002, but the United States has balked at the demands.

Since, opposition members of Parliament, provincial government heads, and forestry company executives asked Canadian Prime Minister Paul Martin to start playing "hardball" with the United States, some even suggesting the need to impose an export tax on Canada's coveted oil and gas resources.