Reaction and updates following the release of more than 250,000 classified US diplomatic cables from WikiLeaks. Tomorrow, revelations about North Korea and the UK.

6.15pm: It is, without a doubt, the biggest leak of secret diplomatic missives in the history of international relations – a total of 251,287 cables from more than 250 US embassies and consulates around the world, many of them frank, a number of them shocking and all of them previously secret.

Over the coming days the Guardian will publish extracts from the cables, obtained by the whistleblowing website Wikileaks, along with its international partners, the New York Times, Le Monde, El País and Der Spiegel.

Even today there's a lot to read through so here's a brief precis of the initial revelations:

• The US is engaged in a spying campaign against the leadership of the United Nations. A directive issued under Hillary Clinton's name last year ordered American diplomats to seek details about both UN communication systems and personal details for top officials.

• Saudi Arabia's King Abdullah has "frequently" urged the US to launch an attack against Iran in order to scupper Tehran's nuclear ambition.

• The US has relentlessly pressured other countries, including close allies such as Italy and France, to distance themselves from Iran and assist American efforts to isolate Tehran

• There's plenty more to come, including "claims of inappropriate behaviour" by a British royal and allegations of links between Russia's government and organised crime.

6.17pm: This is, of course, the latest in a series of revelations published in collaboration with Wikileaks, following on from the Iraq and then Afghanistan war logs. Reaction has already begun ahead of the release of the embassy cables. In an unusual move, the US government has released a letter from the state department to the Wikileaks founder, Julian Assange, warning that making the files public would poison international relations and jeopardise lives.

State department legal adviser Harold Koh said publication will "place at risk the lives of countless innocent individuals" as well as affecting "on-going military operations" and "on-going cooperation between countries".

He wrote:

They were provided in violation of U.S. law and without regard for the grave consequences of this action.

David Cameron is among a series of world leaders already briefed about the likely revelations by state department officials. UK newspaper editors were asked on Friday to inform the government if they planned to publish the files, although the government has no plans to try and formally suppress them.

6.22pm: The Foreign Office has already condemned the release of the information. An FCO spokesman said:

We condemn any unauthorised release of this classified information, just as we condemn leaks of classified material in the UK. They can damage national security, are not in the national interest and, as the US have said, may put lives at risk. We have a very strong relationship with the US government. That will continue.

6.24pm: In contrast to the Foreign Office's measured tone, Italy's foreign minister, Franco Frattini, has rather colourfully described the embassy cables as "the September 11th of world diplomacy". Speaking on a visit to Qatar, he was quoted as saying that the information would "blow up the relationship of trust between states".

6.27pm: Here's the cover of Der Spiegel's initial take of the story. Some of the captions attached to luminaries on the cover, taken from US embassy cables, include "Avoids risk, rarely creative" (for Angela Merkel) and, more intrguingly still, "Luxuriant blonde nurse" (Libya's Muammar Gaddafi). The English version of their story is here.

6.32pm: It's also worth mentioning, as widely reported elsewhere, that Wikileaks has alleged that its website, which many internet users had not been able to access over the day, had been deliberately targeted. "We are currently under a mass distributed denial of service attack," it said in a tweet.

6.47pm:

Mark Tran taking over from Peter Walker. I'll be following reaction over the next few hours. Responses are coming in thick and fast. Here is a statement from the White House.

We anticipate the release of what are claimed to be several hundred thousand classified State department cables on Sunday night that detail private diplomatic discussions with foreign governments. By its very nature, field reporting to Washington is candid and often incomplete information. It is not an expression of policy, nor does it always shape final policy decisions. Nevertheless, these cables could compromise private discussions with foreign governments and opposition leaders, and when the substance of private conversations is printed on the front pages of newspapers across the world, it can deeply impact not only US foreign policy interests, but those of our allies and friends around the world. To be clear - such disclosures put at risk our diplomats, intelligence professionals, and people around the world who come to the United States for assistance in promoting democracy and open government. These documents also may include named individuals who in many cases live and work under oppressive regimes and who are trying to create more open and free societies. President Obama supports responsible, accountable, and open government at home and around the world, but this reckless and dangerous action runs counter to that goal. By releasing stolen and classified documents, Wikileaks has put at risk not only the cause of human rights but also the lives and work of these individuals. We condemn in the strongest terms the unauthorized disclosure of classified documents and sensitive national security information.

6.59pm:

Clinton argues that the disclosures put at risk US diplomats, intelligence professionals and others. This is how the New York Times and the Guardian address the issue.

The Guardian says: "There are some cables the Guardian will not be releasing or reporting owing to the nature of sourcing or subject matter. Our domestic libel laws impose a special burden on British publishers."

The New York Times says it has taken similar precautionary measures and gives this justification for publication of the story.

But the more important reason to publish these articles is that the cables tell the unvarnished story of how the government makes its biggest decisions, the decisions that cost the country most heavily in lives and money. They shed light on the motivations — and, in some cases, duplicity — of allies on the receiving end of American courtship and foreign aid. They illuminate the diplomacy surrounding two current wars and several countries, like Pakistan and Yemen, where American military involvement is growing. As daunting as it is to publish such material over official objections, it would be presumptuous to conclude that Americans have no right to know what is being done in their name.

7.02pm:

The White House has accused WikiLeaks' of "reckless and dangerous action" and says the move endanger lives and risk hurting relations with friendly countries.

7.43pm:

Here is a summary of all of today's stories from the Guardian's first day of coverage of this major story:

• The US faces a worldwide diplomatic crisis. More than 250,000 classified cables from American embassies are leaked, many sent as recently as February.

• Saudi Arabia puts pressure on the US to attack Iran. Other Arab allies have secretly agitated for military action against Tehran.

• Washington is running a secret intelligence campaign targeted at the leadership of the United Nations, including the secretary general, Ban Ki-moon, and the permanent security council representatives from China, Russia, France and the UK.

• The round-the-clock offensive by US government officials, politicians, diplomats and military officers to curb Iran's nuclear ambitions and roll back its advance across the Middle East.

• Israel regarded 2010 as a "critical year" for tackling Iran's alleged quest for nuclear weapons and has warned the United States that time is running out to stop Iran from acquiring a nuclear bomb.

• The secret EU plot to boycott the inauguration of Mahmoud Ahmadinejad as president after the disputed Iranian election in 2009.

• IAEA officials denied blueprints and told by Iran that evidence of bomb-grade uranium enrichment was forged.

• Saudi Arabia complains directly to the Iranian foreign minister of Iranian "meddling" in the Middle East.

• US accuses Iran of abusing the strict neutrality of the Iranian Red Crescent (IRC) society to smuggle intelligence agents and weapons into other countries, including Lebanon.

• Britain's ambassador to Iran gave the US a private masterclass on how to negotiate with Iran.

• How a 75-year-old American of Iranian descent rode a horse over a freezing mountain range into Turkey after officials confiscated his passport.

• How the 250,000 US embassy cables were leaked.

• Siprnet: where America stores its secret cables.

• Editor's note: publishing the cables.

• Browse the data base.

7.45pm:

The US ambassador to the UK, Louis Susman, has issued this tough statement.

Releasing documents of this kind place at risk the lives of innocent individuals – from journalists to human rights activists and bloggers to soldiers and diplomats. It is reprehensible for any individual or organization to attempt to gain notoriety at the expense of people who had every expectation of privacy in sharing information.

7.48pm:

The Democratic chairman of the Senate foreign relations committee, John Kerry, rejects comparisons with the leak of the Pentagon papers during the Vietnam war.

This is not an academic exercise about freedom of information and it is not akin to the release of the Pentagon Papers, which involved an analysis aimed at saving American lives and exposing government deception. Instead, these sensitive cables contain candid assessments and analysis of ongoing matters and they should remain confidential to protect the ability of the government to conduct lawful business with the private candor that's vital to effective diplomacy.

7.53pm:

Here is the New York Times laying out some of the topics it will cover in the coming days. They include a dangerous standoff with Pakistan over nuclear fuel, gaming out an eventual collapse of North Korea and allegations against China of global hacking.

7.59pm:

Le Monde justifies its decision to cover the classified cables by arguing that to inform does not mean to act irresponsibly. Transparency and judgment (Le Monde uses the word discernement) are not incompatible, the paper says, which is what distinguishes it from WikiLeaks.

8.20pm:

The Guardian's editor, Alan Rusbridger, will be online tomorrow at 4pm to take questions on the paper's decision to cover this story. Meanwhile, Guardian columnist Simon Jenkins rejects claims by the US and other governments that the stories threaten national security.

The revelations do not have the startling, coldblooded immediacy of the WikiLeaks war logs from Iraq and Afghanistan, with their astonishing insight into the minds of fighting men seemingly detached from the ethics of war. The disclosures are largely of analysis and high-grade gossip. Insofar as they are sensational, it is in showing the corruption and mendacity of those in power, and the mismatch between what they claim and what they do... Clearly, it is for governments, not journalists, to protect public secrets. Were there some overriding national jeopardy in revealing them, greater restraint might be in order. There is no such overriding jeopardy, except from the policies themselves as revealed. Where it is doing the right thing, a great power should be robust against embarrassment.

8.32pm:

US embassy officials in Berlin will have to soothe ruffled feathers of top German officials if they haven't done so already. Der Spiegel highlights the negative American assessments of the German foreign minister, Guido Westerwelle.

The secret reports describe him as incompetent, vain and critical of America. The US diplomats report that they face a challenge in dealing with a politician who is considered an "enigma," who has little foreign policy experience and "remains skeptical about the US." An embassy cable from Berlin from Sept. 22, 2009 describes Westerwelle as having an "exuberant personality." That is why he finds it difficult to take a backseat when it comes to any matters of dispute with Chancellor Angela Merkel," the cable says.

8.53pm:

The Israeli paper, Haaretz focuses on the June 2009 memo. This quotes Israel's defence minister, Ehud Barak, telling visiting American officials that a strike on Iran's nuclear facilities was viable until the end of 2010, but after that "any military solution would result in unacceptable collateral damage."

Little in the way of reaction from Iran, where it has gone midnight, so far. Press TV mentions in its breaking news strap, but that's it. The revelations about Iran do show how unpopular Tehran is in the Arab world. It will be interesting to see whether the disclosures will prompt Iran to soften its image - perhaps launch a charm offensive - or reinforce its hard line.

9.03pm:

Reuters has a round-up of some reaction. Views are mixed, ranging from alarm to "it's no big deal". Cox, one suspects, has it about right.

Roger Cressey, a partner at Goodharbor Consulting: "This is pretty devastating. The essence of our foreign policy is our ability to talk straight and honest with our foreign counterparts and to keep those conversations out of the public domain. This massive leak puts that most basic of diplomatic requirements at risk in the future. Think of relations with Saudi Arabia, Yemen and Afghanistan, governments who we need to work with us in defeating al Qaida. Their performance has been uneven in the past, for a variety of reasons, but this kind of leak will seriously hinder our ability to persuade these governments to support our counterterrorism priorities in the future."

Christopher Meyer, the former British ambassador to the US: "This won't restrain dips' (diplomats) candour. But people will be looking at the security of electronic communication and archives. Paper would have been impossible to steal in these quantities."

Professor Michael Cox, associate fellow, Chatham House thinktank: "It's a great treasure trove for historians and students of international relations. It is a sign that in the information age, it is very difficult to keep anything secret. But as to whether it's going to cause the kind of seismic collapse of international relations that governments have been talking about, I somehow doubt. Diplomats have always said rude things about each other in private, and everyone has always known that. Governments have a tendency to try to keep as much information as possible secret or classified, whether it really needs to be or not. The really secret information, I would suggest, is still pretty safe and probably won't end up on WikiLeaks.

9.35pm:

The New York Times has a revealing exchange of letters between various senior government officials and Julian Assange, the founder of WikiLeaks. The administration argues that the leaked cables will endanger lives and national security. Assange responds by saying that the "supposed risks are fanciful" and argues that the US is more concerned to "suppress evidence of human rights abuses and criminal behaviour".

9.55pm:

Somebody is happy.

"Oh goody goody gumdrops. NINE DAYS of wikileaks cables coverage from @nytimes http://ow.ly/3gvq9," tweets Katherine Tiedemann@afpakchannel.

10.17pm:

I'm finishing now, but Matthew Weaver will resume live blogging early tomorrow morning on this story as the world digests the first batch of these classified US cables - 250,000 of them. There will be more - much more to come - in the next few days. The Guardian's editor, Alan Rusbridger, will be responding to questions live online at 4pm tomorrow. Thanks for all your comments.