Leading Europeans, from Angela Merkel down to information chiefs across the continent, are lining up to grill American counterparts on the Prism surveillance programmes, amid mounting fury that the private information of EU nationals will have been caught up in the data dragnet.

With Merkel set to bring up the issue with Barack Obama next week, and the European commission vice-president, Viviane Reding, eager to grill US officials at a meeting in Dublin on Friday, the issue looks set to dominate a week of summitry. Reding, who is responsible for data protection in Europe, is to seek clarification on whether the access to personal data in the Prism programme is limited to individual cases, is based on concrete suspicion or if wider sets of data are being accessed.

Peter Schaar, Germany's federal data protection commissioner, told the Guardian that it was unacceptable for the US authorities to have access to EU citizens' data and that the level of protection was lower than that guaranteed to US citizens.

"So far, the US has no adequate level of data protection guaranteed in law and with independent oversight, like in Europe," he told the Guardian. "It's essential for me that we cannot ignore anymore the question of what happens with the data of the private sector if it's collected by US or third-party companies and public authorities want to surveil this data.

"I don't know how far European governments are informed over the details of US authorities to the data, but one problem might be that the data gathered by the US authorities comes back from the US to Europe and is used by European authorities. We have to discuss this with our governments."

Michael Hartmann, spokesman on domestic issues for Germany's opposition Social Democratic Party (SPD), said he would be seeking clarifications on Wednesday from the German secret service on what the government knew and when. "We want to know what the government knew about it and whether there was any benefit for the German authorities in what the US authorities did," he told the Guardian. "We can't accept this although we know that after 9/11 there were new rules and we have to be careful and well informed, but you can't defend our free society by destroying it."

Antonello Soro, head of the Italian data-protection authority, said he was "very concerned" by the consequences of the surveillance on the privacy of European and Italian citizens.

"A gathering of data of this capacity, so indiscriminate and generalised, going beyond any evidence of crime, would not be legal in Italy and, if it were to happen, would be contrary to the principles of our legislation and would represent a very serious violation," he told the Guardian in a statement.

EU commission officials say that where the privacy rights of a European citizen are concerned, it is for a judge in their member state to determine whether the data can be lawfully transmitted. They warn that simply relying on US or other "third-country" law may be breach international law. They say that such transmission of personal data should be done through established official channels such as mutual legal-assistance agreements.

The EU's new proposed data-protection regime makes it clear that companies, such as US internet firms, providing services to people in Europe would be bound by the obligations of European law.

EU officials have already raised the issue with the Americans and have been pressing for European citizens to have the same rights of access to judicial redress if their personal data is mishandled, as is afforded to US residents. They say they have repeatedly raised the issue of European citizens' data held by private companies, including internet and phone companies, being accessed by US law-enforcement agencies under the Patriot Act and the Foreign Intelligence Surveillance Act.

Reding said the EU's data-protection proposals had been on the table for 18 months now, with many EU states stalling on their implementation. She contrasted the fact noted that it took only six months for EU ministers to bring in "data retention" powers requiring phone and internet firms to store users' records for 12 months.

The Italian government came under pressure to establish the extent to which Italian citizens had been affected by the surveillance system. Franco Pizzetti, chairman of the digital development group Internet Alliance and Italy's former data protection authority chief, wrote to the prime minister, Enrico Letta, demanding he respond to the revelations.

"If what we are reading is, either partially or wholly true, this is a question of very serious violations of Italian and European citizens' basic rights," he wrote. Pizzetti told the Guardian that he believed it was "impossible" that Italian citizens' data had not been caught up in the US National Security Agency's activities. "Both the Italian government and the European commission should ask the United States for clarification," he said. "The Italian and European authorities should ask for information and explanations from [the technology giants] because they allowed access to European citizens' data without informing European citizens, violating the rules on personal data protection."

The French Socialist Euro MP, Françoise Castex, said she was shocked that the Americans had been snooping on European citizens even while negotiating with the European Union for the right to do so. "Even before we had said yes or no, they had decided to do it anyway," Castex told the Guardian.

"We in Europe had been arguing that personal information of our citizens should not be freely used by American businesses. We felt this should not happen; we should not say yes to this. We were under a lot of pressure and lobbying from the American Chamber of Commerce and giant American companies like Google, Facebook and Apple to ease the restrictions over the use of personal data. And there they were taking it anyway.

"I suppose we cannot say we are terribly surprised but it's still a shock. A shock that they have gone outside all agreements, even before those agreements are reached."Of course you can try to justify these things by saying 'well, if you're not a terrorist you have nothing to worry about' and of course there are security concerns that require some information. But you and I know full well that as soon as this information is gathered it won't be used for security or defence ends, it will be used for commercial ends.

"Personal data is the material of the 21st century and is worth a lot. People who say it doesn't matter are being naive.

"There is a serious threat to public liberty here. This is information that should rest confidential. I don't want my sexual orientation, any addictions like gambling I might have, any illnesses collected and sold to anyone. These are things that could be used against us by an employer or insurance company." Kai Biermann, a journalist at the German weekly newspaper, Die Zeit, said: "It surprised nobody, because everyone assumes the NSA had been doing something like this for a long time. It's almost a meme – the idea that the NSA has the whole world under surveillance. It doesn't surprise me but it is still frightening when you see it laid out in front of you.

"There were two recent cases in Germany, where tip-offs from the USA led to terror warnings and investigations. It was said that they received information from the FBI, that was the statement, from captured emails. The idea that Prism could've been behind that is not a far-fetched one."

Russian authorities remained mute on the revelations, a silence that analysts said reflected their own approach towards internet privacy.

Andrei Soldatov, an analyst who focuses on Russia's secret services and the internet, said: "The main point for me in all this is that it provides ammunition to those who argue for sovereign internet in their countries – Russia, China, Iran, African states and so forth. I don't think in practical terms it's a real big danger for Russian government bodies, because of the Russian policy to count on Russian-made technology in government communications, or on western technology licensed by the secret services. But it does provide new arguments for regionalists."

Canada's privacy commissioner, Jennifer Stoddart, said she has had significant concerns about the NSA surveillance programme and was proposing an international summit of privacy watchdogs to mount a concerted defence of personal information that is being collected using the computer and telephone usage records of private companies. The fear is acute in Canada, where the border between the two countries means Canadians are foreign citizens and likely to have their communications intercepted, but geography and economics dictate that vast amounts of metadata will continue to flow through US servers.A newspaper report on Monday revealed that the NSA's Ottawa-based sister agency, the Communications Security Establishment, had in 2011 obtained secret authority to resurrect its made-in-Canada data-surveillance programme, which was created in 2005 but fell dormant in 2008. The CSE monitors foreign intelligence for the Canadian military, police and spy agencies, but says that any Canadian information caught in its net is rendered anonymous by law.

In Pakistan, attention focused on the extraordinary volume of data being gathered from computers and telephone networks by the NSA.

In one sample month, March 2013, Pakistan was second only to Iran in the snooped-on top 10. "US stole 13.5bn Pak secret reports," was one headline on The News, a right-of-centre newspaper known for its anti-Americanism.Pakistanis are already used to their country being of intense interest to the US intelligence community but there are concerns about what the NSA's electronic spying means for non-US citizens who do not enjoy rights under the US constitution.

"For those of us living outside the US, the concern should be that, in the future, a simple internet search could potentially be used to build a damning case," an editorial in Monday's Express Tribune said.

"Given the manner in which the US has pursued terror suspects – imprisoning some on very flimsy evidence – this should set off alarm bells."

In Egypt, Amr Gharbeia, a prominent campaigner for internet freedom and civil liberties director at the Egyptian Institute for Personal Rights, said it was surprising how much Egyptian data had been gathered (7.6bn pieces of information in March 2013).

"What struck me is that knowing how people use the internet in Egypt, and what the rate of penetration is like – which is not as much as you get in a developed country – the amount of times they have come here and looked for information is staggering.

"One can only wonder who the entity is that is making use of this kind of information. Is it only the NSA or CIA, or are there links to the Egyptian intelligence agencies? Given that the Egyptian intelligence and CIA have a long history of co-operation in their war against terrorism … one can only extrapolate from that and assume safely that there is a very good relationship between the two countries' national security agencies."

In sub-Saharan Africa, Dale McKinley, a spokesman for South Africa's Right2Know campaign, a civil society group defending freedom of information, said: "We're not at all surprised. It's been known for some time that this kind of snooping and surveillance of electronic communications was happening. But it's good to have it confirmed."

He warned: "South Africans should be worried. Africa is now an area of increasing strategic and economic importance and will become more so. The intelligence to carry out policy is going to be even more necessary."

Louise Mushikiwabo, foreign minister of Rwanda, said: "Does it surprise anybody that the United States' NSA would access information of internet users, and otherwise? For Rwanda, we believe state and other actual 'secrets' are better handled away from the internet, but, oh well ... it is almost inevitable to be on the internet these days."

Bitange Ndemo, former permanent secretary in Kenya's information ministry, said: "It is a cause for concern since it touches on the privacy of the people. Our national security will look at the matter before making a substantive statement."

George Charamba, press secretary to Zimbabwe's President Robert Mugabe, said it was an unsurprising aspect of US attempts at "world domination". He added: "When we went to the UN World Summit on Information Society in Geneva, there was a very strong pursuit to look at the governance of ICT [information and communications technology]. The Americans were very robust in rejecting that. They were very belligerent about it.

"There is nothing extraordinary in the revelation that Americans are monitoring personal data. We just have to adjust to the threat. It's a pity for you guys in the media: issues of freedom of expression play second fiddle to other considerations. It goes to the heart of the whole issue of liberal democracy."

Jon Boone in Islamabad, Miriam Elder in Moscow, Patrick Kingsley in Cairo, Kim Willsher in Paris, David Smith in Johannesburg and Allan Woods in Montreal contributed to this report