The Intercept's latest disclosure of classified documents revealed the UK Government Communications Headquarters (GCHQ) and the US National Security Agency (NSA) stole Gemalto's encryption keys in 2010 and monitored its SIM card users' mobile phone activities.
"We have several suppliers, and Gemalto is one of them," Tele2 spokesperson told Sputnik via telephone, adding that a joint investigation with Gemalto is underway.
"At the moment [we] cannot say what the number of victims is," the spokesperson said.
Britain's Vodafone also told Sputnik it offered Gemalto its assistance into the alleged GCHQ and NSA hack soon after the revelations gained circulation in the media.
Elsewhere, Germany's Deutsche Telekom expressed concern that its customer base may have fallen victim to the attack, while Russia's two largest mobile phone operators ruled out substantial security concerns involving their users.
Other major operators using Amsterdam-based Gemalto's SIM cards include AT&T, T-Mobile, Verizon and Sprint.
The latest revelations are part of 1.7 million classified documents leaked by former NSA contractor Edward Snowden in July 2013, setting off a US mass surveillance scandal.