OTTAWA — Canadian opposition politicians expressed shock and anger on Thursday over a report that the National Security Agency conducted widespread surveillance during a summit meeting of world leaders in Canada in June 2010.

The Canadian Broadcasting Corporation, citing a confidential briefing paper obtained by Edward J. Snowden, the former N.S.A. contractor, reported on Wednesday night that the N.S.A. turned the United States Embassy in Ottawa into a command post for a six-day surveillance operation that coincided with the Group of 20 summit meeting in Toronto and the Group of 8 meeting in Huntsville, Ontario.

According to the document, the operation was “closely coordinated with the Canadian partner,” an apparent reference to the Communications Security Establishment Canada, a Canadian electronic surveillance agency.

Exactly who or what the N.S.A. was monitoring, however, was unclear from the CBC’s description of the report. The document does indicate, however, that the N.S.A. believed that its mandate during the summit meetings included “providing support to policy makers.”