Washington 'bugged key EU offices' - German magazine
Germany's Der Spiegel magazine says it has seen a secret document showing the US has bugged EU offices in Washington and at UN headquarters in New York.
The paper says it was shown the 2010 "top secret" document by fugitive ex-security analyst Edward Snowden.
The US National Security Agency document allegedly outlined how it spied on EU internal computer networks, referring to the bloc as a "target".
An EU official said the claim could have a "severe impact" on EU-US ties.
"On behalf of the European Parliament, I demand full clarification and require further information speedily from the US authorities with regard to these allegations," Martin Schulz, the President of the European Parliament said in a statement, according to Reuters news agency.
The US has so far made no public comments on the Spiegel's claim.
Mr Snowden - a US citizen - has requested asylum in Ecuador.
He is believed to be staying at Moscow's airport, having arrived there last weekend from Hong Kong, where he had been staying since he revealed details of top secret US surveillance programmes.
The US has charged him with theft of government property, unauthorised communication of national defence information and wilful communication of classified communications intelligence.
Each charge carries a maximum 10-year prison sentence.
On Saturday, US Vice-President Joe Biden and Ecuadorian President Rafael Correa held a telephone conversation about Mr Snowden's asylum request.
According to Mr Correa, Mr Biden had "passed on a polite request from the United States to reject the request".
The Ecuadorian leader said his answer was: "Mr vice-president, thanks for calling. We hold the United States in high regard. We did not seek to be in this situation."
If Mr Snowden ever came to "Ecuadoran soil" with his request, he added, "the first people whose opinion we will seek is that of the United States".
The Ecuadorean president, a left-wing economist who received a doctorate in the US, denied he was seeking to disrupt relations and said he had "lived the happiest days of my life" in the US.
Quito earlier said it was willing to consider Mr Snowden's request but only when he was physically in the Latin American country.
White House spokeswoman Bernadette Meehan said only that Mr Biden and Mr Correa had held a wide-ranging conversation.
20 May: Snowden flies from Hawaii to Hong Kong.
5 June: From Hong Kong, Snowden discloses details of what he describes as a vast US phone and internet surveillance programme to the UK's Guardian newspaper.
23 June: Snowden leaves Hong Kong on a flight to Moscow. He is currently thought to remain airside at Sheremetyevo airport.
From Moscow, Snowden could fly to Cuba, en route to Ecuador, which has said it is "analysing" whether to grant him asylum.
Venezuela had also been considered a possible destination for Snowden, however it is thought he would only pass through on his way to Ecuador.
Snowden is reported to have requested asylum in Ecuador, which previously granted haven to Wikileaks founder Julian Assange in its London embassy.