"The NSA spied on members of the Spanish government," the source told El País newspaper.
"US spy agencies used the same practices in many countries. And Spain has been no exception," that source added.
The Spanish government now fears that current Prime Minister Mariano Rajoy and his predecessor José Luis Rodríguez Zapatero may be among the figures spied upon, the paper reported.
The country's Foreign Ministry plans to call in the US Ambassador to Spain James Costos when further details of US spy activity in the country becomes apparent, El País said.
Friday's report in El País report is the paper's second this week alleging the US spied on Spain.
On Tuesday, the centre-left daily quoted sources within Spain's security services as saying they believed the US systematically spied on telephone calls, emails and SMS messages in Spain.
The paper said that information was based on information provided by NSA whistle-blower Edward Snowden, a former US spy agency contractor wanted by Washington but currently at an unknown location in Moscow.
The newest El País report comes in the midst of a diplomatic row between European leaders and the US over spying.
Berlin and Paris called on Washington on Friday to agree on rules in the spy game after recent revelations that the US tapped German Chancellor Angela Merkel's mobile phone and that the country collected metadata on 70 million calls made in France.
The leaders of the 28-state European Union "took note of the intention of France and Germany to seek bilateral talks with the United States" on what their secret services should and cannot do, EU President Herman Van Rompuy told a press conference after a first night of summit talks on the matter.
Merkel had arrived at the two-day talks saying: "Spying between friends, that's just not done" after reports the US NSA had listened in her calls.
In a turn of events that is unlikely to calm the situation, the Guardian newspaper on Friday reported information from documents provided by Snowden showing that the NSA had monitored the phone conversations of 35 world leaders.
This spying was carried out after numbers were passed on by an official in another US government department, the leaked memo published in the Guardian showed.
The Guardian has been spearheading the media reports on spying by the NSA after Snowden shared information with Glenn Greenwald, a journalist at the paper.
Greenwald first flagged upcoming leaks on Spain on October 9th while giving testimony before a Brazilian congressional panel.
On October 14th, the journalist said four or five new stories that involve Spain and France would be published soon.
"There's no way to stop this process now. We're going to publish to the last document," he said.
Greenwald has previously snubbed claims he should be releasing all of the information he holds at the same time.
"Those documents are being worked on and now they are in the hands of other people," he said.
"If something were to happen, that information is still available and can be used."