Efforts to secure the release of the UN envoy to Niger Robert Fowler, his assistant and their driver, who disappeared without trace in the West African country two weeks ago, have been shrouded in secrecy.

Canada's foreign ministry has declined to comment on its diplomatic mission to ensure Fowler's release, even to the point of refusing to confirm that Canada's ambassador to the Ivory Coast had travelled to Niger, although this was confirmed by the embassy in Abdijan.

Authorities in Niger have said they are doing all they can to locate Fowler and his assistant Louis Guay.

However, neither side has reported the slightest progress.

The men's car was discovered December 15 at the side of the road in an apparently trouble-free area close to the capital Niamey. It's engine was running, with the indicator on. The vehicle's doors were wide open.

Three mobile phones, a camera and a jacket had been left inside.

The men, both Canadian diplomats, were returning from a visit the previous day to a gold mine operated by Canadian company Semafo west of Niamey.

The alarm was raised in the early hours of Monday morning when they did not return to the capital.

A Tuareg rebel group initially said it had kidnapped the men, before retracting the claim the same day.

The Niger authorities initially confined themselves to saying Fowler had not requested permission to make the trip to the mine.

However, appearing to take stock of the harm done to Niger's image, they issued a new statement saying all possible measures were being taken to find the two men.

Investigators have also combed the river Niger, which flows through the area where the men disappeared. Their trip, to the Samira area, entailed crossing the river by ferry.

But for the past week no-one has wanted to talk about Fowler's disappearance, even on background.

"It's the sort of case best handled between two capitals," said a diplomat in Niamey.

"We don't have anything concrete, all our searches so far have been in vain. We're not ruling out any hypothesis ranging from a simple criminal kidnapping to a political kidnapping, but so far nothing has been conclusive," the official said.

The Canadian in charge of the Samira mine told AFP Fowler and Guay did indeed visit on Sunday 14th December, the day before they were reported missing.

Officials in Ottawa are no more talkative than their Niger counterparts.

At the beginning of this week Lisa Monette, a spokeswoman for Canada's foreign affairs ministry said the authorities did not intend to comment on their "relations with the Niger authorities" or their "efforts in Niger."

She declined even to confirm Canada's ambassador to Abidjan had travelled to Niger, even after the embassy in Abidjan confirmed the trip.

UN officials have declined to comment, beyond confirming that Fowler was on an official trip, contradicting the Niger government version that his visit was private.