A new set of classified documents disclosed Sunday suggested that Edward J. Snowden, the former National Security Agency contractor who has provided a trove of documents to The Guardian newspaper, had obtained a wider range of materials about government surveillance than had been known, including one document revealing how American and British intelligence agencies had eavesdropped on world leaders at conferences in London in 2009.

The latest disclosures, appearing again in The Guardian, came the night before a meeting of the Group of 8 industrialized nations was to open in Northern Ireland, where some of the leaders who were intelligence targets four years ago will be in attendance.

The newspaper reported Sunday night that Government Communications Headquarters, or G.C.H.Q., the British eavesdropping agency that works closely with the N.S.A., monitored the e-mail and phones of other countries’ representatives at two London conferences, in part by setting up a monitored Internet cafe for the participants. In addition, the United States intercepted the communications of Dmitri A. Medvedev, then the Russian president and now the prime minister, the newspaper said.

The Guardian posted some G.C.H.Q. documents on its Web site with part of the contents blacked out. A spokesman for The Guardian said Sunday that the paper decided to redact the documents, and that enough was published “to show the authenticity of the report.”