The White House has insisted that the US "is not monitoring and will not monitor" the communications of German chancellor Angela Merkel.

The German Foreign Ministry has summoned the US ambassador in the wake of allegations that American intelligence may have targeted Chancellor Angela Merkel's mobile phone.

Ambassador John B Emerson is expected to meet Foreign Minister Guido Westerwelle, who will "spell out the position of the German government".

The US Embassy said it had no comment.

Mrs Merkel's government says she complained to President Barack Obama in a phone call on Wednesday after receiving information her phone may have been monitored.

The White House said it isn't monitoring and won't monitor Mrs Merkel's communications, but conspicuously didn't say that they were never monitored.

German spokesman Steffen Seibert said Mrs Merkel made clear in her call that "she views such practices, if the indications are confirmed ... as completely unacceptable" and called for US authorities to clarify the extent of surveillance in Germany.

A statement from Mr Seibert said the German government "has received information that the chancellor's cellphone may be monitored by American intelligence".

News magazine Der Spiegel, which has published material from NSA leaker Edward Snowden, said its research triggered the response.

White House spokesman Jay Carney said the US is examining Germany's concerns as part of a review of how the US gathers intelligence.

The White House has cited that review in responding to similar spying concerns from France and other US allies.