The widespread surveillance of Spanish citizens by the US National Security Agency, which caused outrage when it was reported this week, was the product of a collaboration with Spain's intelligence services, according to one Spanish newspaper.

In the latest revelations to emerge from the documents leaked by the US whistleblower Edward Snowden, Spanish agents not only knew about the work of the NSA but also facilitated it, El Mundo reports.

An NSA document entitled "Sharing computer network operations cryptologic information with foreign partners" reportedly shows how the US relies on the collaboration of many countries to give it access to intelligence information, including electronic metadata.

According to the document seen by El Mundo, the US classifies cooperation with various countries on four different levels. In the first group – "Comprehensive Cooperation" – are the UK, Australia, Canada and New Zealand. The second group – "Focused Cooperation" – of which Spain is a member, includes 19 countries, all of them European, apart from Japan and South Korea. The third group – "Limited cooperation" – consists of countries such as France, Israel, India and Pakistan; while the fourth – "Exceptional Cooperation" – is made up of countries that the US considers to be hostile to its interests.

The reports come a day after the director of the NSA, General Keith B Alexander, testified before the US house intelligence committee that suggestions the agency monitored millions of calls in Spain, France and Italy were "completely false" and that this data had been at least partially collected by the intelligence services of those countries and then passed on to the NSA.

According to El Mundo the NSA documents explain the "specific guidance for evaluating and initiating Computer Network Operations (CNO) cryptologic cooperation with other countries, generally within existing foreign cryptologic relationships". It outlines these telephonic and electronic surveillance operations, indicating that the results would be shared with allied countries. In short, this suggests the Spanish intelligence services were working hand in hand with the NSA, as were other foreign agencies. But if there was any doubt as to who held the upper hand, the NSA documents make clear that any collaboration was always to serve the needs of protecting American interests.

On Monday, El Mundo reported that the NSA had intercepted 60.5m phone calls in Spain over one month alone.

Alexander said foreign intelligence services collected phone records in war zones and other areas outside their borders and passed these on to the NSA. He said this arrangement had been misunderstood by French and Spanish newspapers, which reported that the NSA was spying in their countries.

But this explanation has not allayed European or domestic US concerns about the exact nature of NSA surveillance in allied countries.

The suggestion that the Spanish intelligence agency was working with the NSA will confirm the suspicions of many in Spain who believe that the government has not only failed to protect its own citizens' privacy, but was actively supportive of US surveillance inside the country.

Although there are strong privacy laws in Spain, and judicial oversight is required before a phone can be tapped, there are concerns that these laws are applied less than rigorously.

The US has offices for the CIA and the NSA in Madrid.

On Monday, Amnesty International called on the Spanish government to "reflect on its total failure to protect its own citizens' privacy".

The prime minister, Mariano Rajoy, announced on Wednesday that the director of the Spanish national intelligence centre (CNI), Félix Sanz Roldán, would be called to appear before the official secrets committee to explain the activities of the NSA and the CNI. Unlike in the US, however, this meeting will be held behind closed doors.

The latest document, published by El Mundo on Wednesday, shows the NSA to be watchful of any information gathered by countries outside the top tier of allies, which together with the US are known as the "five eyes".

According to the Spanish newspaper's report, the NSA says any co-operation with countries outside this group is to be carefully evaluated, and they should be reliable allies, capable of protecting any US classified information.

A further document seen by El Mundo reportedly explains how that cooperation between the NSA and foreign intelligence agencies increases the number of foreign-language speakers available to it, so as better to understand any communications they uncovered.

Not every line in the document is hard intelligence work, though. At one point, an NSA agent apparently writes that the Spanish agents were exceptionally helpful when they collaborated, not just at work, but also in their downtime. In Madrid, lunch apparently always took place at 2pm; the US agents were given an enjoyable bus tour of the sights of Madrid; and one dinner was accompanied by opera singers. The only disappointment came during one trip to Spain, when it rained all the time, despite the Spanish agents having promised unlimited sunshine.