The possible tapping of German chancellor Angela Merkel’s mobile phone by the US security services is ‘extremely serious’, says Dutch prime minister Mark Rutte.

Speaking in Brussels during the EU summit, Rutte said: ‘If this is true, it is extremely serious. I fully support her protests. This is just not on.’

The revelations that Merkel and thousands of other Europeans have been listened into by the Americans is threatening to overshadow the summit, the BBC said.

1.8 million

Earlier this week, it emerged the NSA may have tapped 1.8 million phone calls in the Netherlands in just one month. Rutte said there are no indications that his mobile calls have been listened into. ‘I don’t know, but there are no indications,’ the prime minister said.

According to the BBC, France and Germany want to hold talks with the US by the end of the year to settle a row over spying.

Rutte said the EU is now in the process of establishing what the US security service NSA has been up to. ‘As allies, we need to get all the facts on the table,’ Rutte said.

Britain’s Guardian newspaper reported that it had obtained a confidential memo from the NSA suggesting it had monitored the phones of 35 world leaders after being given their numbers by a US government official. Whistleblower Edward Snowden was the source of the report.