US Secretary of State Hillary Clinton has denounced the release of classified diplomatic cables as an "attack on the international community".
She spoke after the whistle-blowing website Wikileaks began the release of some 250,000 messages from US envoys around the world.
The cables offer candid and sometimes unflattering views of world leaders and frank assessments of security threats.
But Mrs Clinton said diplomats often needed confidentiality to be effective.
"This disclosure is not just an attack on America's foreign policy interests," she said.
"It is an attack on the international community: the alliances and partnerships, the conversations and negotiations that safeguard global security and advance economic prosperity.
"I am confident that the partnerships that the Obama administration has worked so hard to build, will withstand this challenge."
The White House has ordered government agencies to tighten their handling of classified documents after the latest Wikileaks release.
Attorney General Eric Holder said there was an ongoing criminal investigation into the release and anyone found responsible would be prosecuted.
Mrs Clinton said it was essential that the diplomatic community be able to conduct private communications.
"The work of our diplomats doesn't just benefit Americans but also billions of others around the globe.
"Every country, including the United States, must be able to have candid conversations about the people and nations with whom they deal. And every country, including the United States, must be able to have honest, private dialogue with other countries about issues of common concern."
The cables are a huge sampling of communications between the US State Department and its embassies and consulates around the world.
The messages were sent between 1966 and 2010 but most are from this decade.
Among the revelations is a report that King Abdullah of Saudi Arabia, among other Arab leaders, urged the US to destroy Iran's nuclear facilities.
Iranian President Mahmoud Ahmadinejad dismissed the leak as US propaganda which would not affect Tehran's relations with its neighbours.
Other concerns aired in the cables include the possibility of Pakistani nuclear material falling into the wrong hands, allowing militants to make an atomic weapon. The widespread use of computer hacking by China's government is also reported.
A series of cables earlier this year from the US embassy in Seoul concern the possibility of the collapse of the North Korean regime. China was reported to believe that North Korea was no longer a useful ally and that the peninsula should be unified under the leadership of Seoul.
As to diplomats' portrayals of world leaders, Italian Prime Minister Silvio Berlusconi is said to have been described as feckless, vain and ineffective and sharing a close relationship with the "alpha dog", Russian Prime Minister Vladimir Putin.
President Nicolas Sarkozy of France is said to be thin-skinned and authoritarian, while German Chancellor Angela Merkel is described as risk-averse.
Meanwhile, Libya's Colonel Muammar Gaddafi always travels with a "voluptuous blonde" Ukrainian nurse, according to one of the cables.
European nations have roundly criticised the leaks, with France saying they represent a threat to democratic authority.
Pakistan's foreign ministry, meanwhile, condemned what it called "the irresponsible disclosure of sensitive official documents".
Other issues reportedly covered in the cables are:
- Iranian attempts to adapt North Korean rockets for use as long-range missiles
- Corruption in Afghanistan with concerns heightened when a senior official was found to be carrying more than $52m (£33m) in cash on a foreign trip
- Bargaining to empty the Guantanamo Bay prison camp - including Slovenian diplomats being told to take in a freed prisoner to secure a meeting with President Barack Obama
- Germany being warned in 2007 not to enforce arrest warrants for CIA officers involved in an operation in which an innocent German citizen with the same name as a suspected militant was abducted and held in Afghanistan
- US officials being instructed to spy on the UN leadership by Secretary of State Hillary Clinton
- Alleged links between the Russian government and organised crime, with intelligence agencies using underworld bosses to carry out operations
- Yemen's president talking to General David Petraeus (while he was responsible for US military operations in Central Asia and the Middle East as head of US Central Command) about attacks on Yemeni al-Qaeda bases and saying: "We'll continue saying the bombs are ours, not yours"
- Faltering US attempts to prevent Syria from supplying arms to Hezbollah in Lebanon
In a statement, the White House said: "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.
"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."
The founder of Wikileaks, Julian Assange, said the US authorities were afraid of being held to account.
No-one has been charged with passing the diplomatic files to Wikileaks, but suspicion has fallen on US Army private Bradley Manning, an intelligence analyst arrested in Iraq in June and charged over an earlier leak of classified US documents to Mr Assange's organisation.
The cables release is the third mass Wikileaks release of classified document; it published 77,000 secret US files on the Afghan conflict in July, and 400,000 documents about the Iraq war in October.
Wikileaks argues the release of the documents has shed light on the wars, including allegations of torture and reports that suggest 15,000 additional civilian deaths happened in Iraq.
Clarification, 18 December 2010: This story has been amended to make it clear that Wikileaks have not yet released all 250,000 secret cables said to be in its possession.