There are conflicting reports about when US President Barack Obama knew that the US National Security Agency (NSA) was eavesdropping on German Chancellor Angela Merkel’s mobile phone. 

Bild am Sonntag cited a “US intelligence worker involved in the NSA operation against Merkel”, said NSA chief General Keith Alexander informed Obama in person about it in 2010.

“Obama didn't stop the operation back then but let it continue,” according to Bild.

The NSA denied the report.

“(General) Alexander did not discuss with President Obama in 2010 an alleged foreign intelligence operation involving German Chancellor Merkel, nor has he ever discussed alleged operations involving Chancellor Merkel,” NSA spokeswoman Vanee Vines said.

“News reports claiming otherwise are not true.”

Earlier, it was reported that Mr. Obama had told Chancellor Merkel that he knew nothing of the eavesdropping, that was reported by Spiegel based on the intelligence documents leaked by Edward Snowden.

The reports have led to the worst diplomatic crisis between the two countries since the end of the World War II.