Rice conveyed her "disappointment" over the withdrawal to her Canadian counterpart Pierre Pettigrew when they met on Tuesday at the sidelines of a London meeting on Palestinian reforms.

She was scheduled to visit Canada in the second week of April, but her spokesman Richard Boucher said "the schedules didn't work out".

"We are looking for a date when we can make that happen," Boucher said, without confirming or denying reports that the cancellation was due to problems over missile defence.

Canada said last week it would not participate in US missile defence shield plans after mulling its stand on the issue for more than a year.

Fluctuating ties

Relations between the two neighbours had appeared to warm of late after cooling with the US-led invasion of Iraq in early 2003, in which Canada had declined to participate.

"He (Pettigrew) explained the political process and she (Rice) explained her disappointment but both came out saying they are committed to their defence relationships and working together wherever we can"

US State Department official

Canada's Liberal Prime Minister Paul Martin leads a minority government and his party's lawmakers had lobbied him not to take part in the programme, which is highly unpopular in the country.

The US State Department has not given any possible new dates for Rice's visit to Canada.

A department official, speaking on condition of anonymity, said Rice and Pettigrew met during a reception on the sidelines of the Palestinian meeting and spoke about the missile defence issue.

"He explained the political process and she explained her disappointment but both came out saying they are committed to their defence relationships and working together wherever we can," the official said.

"She said she looked forward to visiting Canada and he said he looked forward to welcoming her," he added.