Queen Elizabeth and the Duke of Edinburgh paid their respects to four RCMP officers killed in an ambush two months ago, and visited a science facility on the third day of their visit to Canada Thursday.

About 500 members of the public lined the entrance to the depot, some waving tiny British flags, but the sombre memorial ceremony in Regina's oldest building, a former mess hall that became a church 110 years ago, was exclusively for family members.

Inside, she met with family members of Const. Peter Schiemann, Const. Brock Myrol, Const. Anthony Gordon and Const. Leo Johnston, killed during a March 3 raid on a farm in rural Alberta.

"She actually spoke of the risks and perils of being a policeman. And how important it is that we still have policemen," Brock's father Keith Myrol, told CBC News.

The Queen and the Duke of Edinburgh then flew to Saskatoon to tour a synchrotron, a football field-sized scientific research facility housing one of the world's most powerful microscopes. Officially opened in October 2004, it is one of 12 such advanced facilities in the world.

Synchrotron executive director William Tomlinson showed the Queen examples of the centre's cancer research and she met members of Teresa McHugh's Grade 6/7 class from Bjorkdale School.

Saskatoon Mayor Don Atchison presented the Queen with the key to the city before the couple attended an evening gala ceremony, considered the grandest event yet on the Royal tour.

The star-studded gala showcased some 700 Saskatchewan performers, with more than 11,000 attending the performance.

The royal couple are to return to Regina tonight.

The pair arrived in Regina on Tuesday as part of a tour to help Alberta and Saskatchewan celebrate 100 years as Canadian provinces.