The US National Security Agency (NSA) logged more than 33 million Norwegian phone conversations over a period of a month last winter, a newspaper said on Tuesday in the first such report involving Norway, a NATO ally.

The report in the Dagbladet daily was based on documents made public by fugitive former NSA contractor Edward Snowden. It was co-authored by Glenn Greenwald, the former Guardian journalist who brought Snowden's leaks to world attention.

Snowden's revelations about the scale of NSA snooping worldwide, on foreign governments and leaders such as German Chancellor Angela Merkel as well as on ordinary citizens, have strained US relations with some of its allies.

According to Dagbladet, information from 33.19 million phone calls were logged between Dec. 10, 2012, and Jan. 8, 2013. Anyone from among Norway's 5.1 million people could have had information about their phone calls recorded, the paper said.

Among European countries, Norway had the largest number of calls logged per capita by the NSA in that period, it added.

Logged information included the length of the calls, who made and received the call, the location of the phones and their serial numbers, said Dagbladet.

"Friends should not spy on one another," Prime Minister Erna Solberg told Norwegian public broadcaster NRK on Tuesday. "It is legitimate to conduct intelligence but it should be targeted and based on suspicions."