Whistleblower website WikiLeaks is set to release some three million documents online, and some of these could potentially damage the US relations with many countries, including Britain and India, according to reports on Saturday.
It is not known what the documents are about, or whether India is mentioned. But State Department spokesman PJ Crowley said, "We have reached out to India to warn them about a possible release of documents."
"We do not know precisely what WikiLeaks has or what it plans to do. We have made our position clear. These documents should not be released," Crowley said.
But in London the Daily Mail reported that among the documents about to be released are secret papers related to the US assessments of then British premier Gordon Brown's personality and his prospects of winning the general election.
Anticipating damages, British Prime Minister David Cameron was warned on Friday night by the US that secrets of the "special relationship" are about to be laid bare, the Daily Mail said.
The US ambassador to London, Louis Susman Friday night made an unprecedented personal visit to Downing Street to warn that WikiLeaks is about to publish secret assessments of what Washington really thinks of Britain.
The website is on the verge of revealing almost three million documents, including thousands of sensitive diplomatic cables sent to Washington from the American embassy in London, according to the Daily Mail.
The bombshell leak is thought to include US assessments of Gordon Brown's personality and his prospects of winning the General Election, and secret discussions on the return of the Lockerbie bomber to Libya.
Assessments of David Cameron's election chances and his private assurances to US officials may also be included, government sources believe.
They fear they will emerge Sunday in coordinated releases in newspapers in Britain, Germany and America.
The British government is so worried that Friday night it issued a D-Notice, warning that publishing the secrets could compromise national security.
The website has previously released secret details of allied military operations in Iraq and Afghanistan.
In total, around 2.7 million confidential messages between the US government and its embassies around the world are to be released.
The US State Department warned that the leaks would damage the US relationships around the world.
Crowley said: "These revelations are harmful to the US and our interests. They are going to create tension in relationships between our diplomats and our friends around the world."
Besides Britain and India, the US has warned the governments of Australia, Canada, Denmark, Norway and Israel in advance of the release.
It has been claimed that a backlash by countries upset over the leaks may lead to US diplomats being expelled.
According to the Britain-based Arabic daily newspaper al-Hayat, the WikiLeaks release includes documents that show Turkey has helped Al Qaeda in Iraq - an extraordinary revelation which could kill off the country's hopes of joining the EU.
The Washington Post reported that the files will contain allegations that the US has supported the PKK, a Kurdish rebel organisation that has been waging a separatist war against Turkey since 1984.
The US says it has known for some time that WikiLeaks held the cables.
No one has been charged with passing them to the website, but suspicion focuses on Bradley Manning, an intelligence analyst arrested in Iraq in June and charged over an earlier leak.
A 10, Downing Street spokesman Saturday declined to discuss the nature of any confidential communications which may have been obtained by WikiLeaks.
But he said: "Obviously, the government has been briefed by US officials, by the US ambassador, as to the likely content of these leaks."
"I don't want to speculate about precisely what is going to be leaked before it is leaked."