Britain's Spanish-owned mobile phone operator O2 and Japan's SoftBank said Thursday that millions of customers were unable to use data due to a glitch.
O2, a division of Spanish telecoms giant Telefonica, blamed a third-party supplier, while Sweden's Ericsson said it had identified an issue that affected a "limited" number of customers in "multiple" countries.
"We're aware that our customers are unable to use data," an O2 spokesman told AFP.
"One of our third party suppliers has identified a global software issue in their system which has impacted us.
"We believe other mobile operators around the world are also affected."
The UK outage began in the early morning and was still ongoing at 1700 GMT.
O2, which has 25 million customers in Britain, also has another seven million people whose mobile providers "piggyback" its network.
SoftBank added that its customers this morning had faced a near five-hour outage "caused by Ericsson-made software errors related to its packet switches, covering our customers nationwide".
The Japanese company also cited an Ericsson report that indicated that telecom carriers in 11 countries were hit.
In Stockholm, Ericsson added it had taken "immediate action" over the incident.
"Following network disturbances in a number of Ericsson's customer networks, Ericsson has taken immediate action to minimize impact and support the restoration of services," it said in a statement.
"Ericsson has identified an issue in certain nodes in the core network resulting in network disturbances for a limited number of customers in multiple countries."
The group's chief executive Borje Ekholm also issued an apology in the late afternoon.
?The faulty software that has caused these issues is being decommissioned and we apologise not only to our customers but also to their customers," Ekholm said.
"We work hard to ensure that our customers can limit the impact and restore their services as soon as possible.?