President Barack Obama was dragged into the trans-Atlantic spying row after it was claimed he personally authorised the monitoring of Angela Merkel’s phone three years ago.

The president allegedly allowed US intelligence to listen to calls from the German Chancellor’s mobile phone after he was briefed on the operation by Keith Alexander, director of the National Security Agency (NSA), in 2010.

The latest claim, reported in the German newspaper Bild am Sonntag, followed reports in Der Spiegel that the surveillance of Mrs Merkel’s phone began as long ago as 2002, when she was still the opposition leader, three years before being elected Chancellor. That monitoring only ended in the weeks before Mr Obama visited Berlin in June this year, the magazine added.

Citing leaked US intelligence documents, it also reported that America conducted eavesdropping operations on the German government from a listening post at its embassy beside the Brandenburg Gate in Berlin, one of more than 80 such centres worldwide.

Mr Obama’s European allies will now ask him to say what he personally knew about the NSA’s global eavesdropping operation and its targeting of world leaders, including those from friendly states. The White House declined to comment on the German media reports.

Last week, however, Mr Obama assured Mrs Merkel that her phone is not being monitored now – and will not be in future. But the US has pointedly declined to discuss the NSA’s actions in the past.

Its surveillance operations raises questions about whether US officials breached domestic laws. Hans-Peter Friedrich, the German interior minister, said: “If the Americans intercepted cellphones in Germany, they broke German law on German soil”. He noted that wiretapping was a crime in Germany and “those responsible must be held accountable”.

Even before the latest reports, German intelligence chiefs were preparing to travel to Washington this week to demand answers from the NSA about the alleged surveillance of Mrs Merkel.

John Kerry, the US secretary of state, received a dose of European fury this weekend when he visited Paris and Rome. The trip was arranged to discuss the Middle East peace process, the Syrian civil war and Iran’s nuclear programme. Instead, he was confronted by outrage over the scale of US surveillance operations.

“The magnitude of the eavesdropping is what shocked us,” said Bernard Kouchner, a former French foreign minister, in a radio interview. “Let’s be honest, we eavesdrop too. Everyone is listening to everyone else. But we don’t have the same means as the United States, which makes us jealous.”

According to the leaked documents in Spiegel, NSA officials acknowledged that any disclosure of the existence of the foreign listening posts would lead to “grave damage” for US relations with other governments.

Such posts exist in 19 European cities, including Paris, Madrid, Rome and Frankfurt, according to the magazine, which has based its reports on documents provided by Edward Snowden, the former NSA contractor.

Mr Obama did not comment, but Republican supporters of the US intelligence community began a fightback on the political talk-shows.

Mike Rogers, the chairman of the intelligence committee in the House of Representatives, said that America’s allies should be grateful for surveillance operations which targeted terrorist threats. “I would argue by the way, if the French citizens knew exactly what that was about, they would be applauding and popping champagne corks,” he told CNN’s State of the Union.

“It’s a good thing. it keeps the French safe. It keeps the US safe. It keeps our European allies safe.”

Peter King, a fellow Republican congressman, said that Mr Obama should not apologise for NSA operations in Europe. “The president should stop apologising, stop being defensive,” he said on NBC’s Meet the Press. “The reality is the NSA has saved thousands of lives not just in the United States but in France, Germany and throughout Europe. Quite frankly, the NSA has done so much for our country and so much for the president, he’s the commander in chief. He should stand with the NSA.”

John Schindler, a former NSA official, noted that planning for the terrorist attacks on Sept 11, 2001 had taken place in Hamburg.

“If 9/11 had happened to Germany and been planned in NY not Hamburg, I’d expect [German] intel to monitor USA top 2 bottom,” he wrote on Twitter.

A German intelligence official, quoted by Die Welt, said: “The Americans did not want to rely exclusively on us after September 11th. That is understandable.”

Another told the newspaper: “Without information from the Americans, there would have been successful terrorist attacks in Germany in the past years.”