Shares in Vodafone have risen after a media report that US mobile operator AT&T was exploring strategies for a potential takeover of the British telecoms firm.

AT&T Chief Executive Randall Stephenson has said there is a "huge opportunity" to invest in mobile broadband in Europe and he would buy wireless assets if they were available at the right price.

AT&T is the second-largest mobile provider in the United States after Verizon Wireless. 

However it is not adding new customers in its home market as fast as Verizon, and it is also ceding market share to much smaller rival T-Mobile US.

Vodafone sold its stake in Verizon Wireless to its joint venture partner Verizon Communications Inc for $130 billion in September, leaving it with a pan-European business spanning Britain to Romania and operations in the Middle East and Africa.

AT&T has been eyeing Europe since the beginning of the year and has considered options including Vodafone and Britain's largest mobile carrier EE, a joint venture of Orange and Deutsche Telekom, sector bankers have previously told Reuters.

A Bloomberg report yesterday, citing people familiar with the situation, said AT&T was examining how it could divide Vodafone up after a deal, keeping some assets and disposing of others. 

The companies have not entered formal negotiations, the report said.

Shares in Vodafone were up 2.9% to 231 p at 11.04am Irish time, the biggest gainers on the FTSE 100 index of blue-chip stocks.

Espirito Santo analyst Robert Grindle said it was logical for AT&T to consider its options regarding Vodafone, following its US exit.

"What we don't have full clarity on is how ambitious AT&T is," he said. "(The report) is short on substance but long on plausibility."

Vodafone and AT&T declined to comment.