Assange had previously warned that if he were detained, he would release so-called "doomsday files" allegedly containing classified information that could threaten American national security, though WikiLeaks said that today's detention will not trigger that release.
"We have over a long period of time distributed encrypted backups of material we have yet to release. All we have to do is release the password to that material, and it is instantly available," Assange told the London Sunday Times before his arrest.
The arrest came after Assange agreed Monday to be interviewed by British police.
Outside the courthouse today, Assange's supporters held signs claiming that today's arrest was politically motivated. It's a charge his accusers' lawyer in Sweden called nonsense.
"Julian Assange knows that what has happened in Stockholm and in the other city with my two clients has nothing whatsoever to do with WikiLeaks or the CIA or the United States or anything like that," said Claes Borgstron, a lawyer for the accusers.
The latest cable leak to anger U.S. authorities includes a list of installations vital to America's national security and interests.
U.S. Defense Secretary Robert Gates, in remarks to reporters Tuesday from Afghanistan, said Assange's arrest is "good news."
U.S. government officials say that the diplomatic leaks have already had an effect on relationships with individuals and governments around the world.
"We have gotten indications that there is at least some change in how individuals and governments cooperate with us, and share information," said Pentagon spokesman Col. Dave Lapan, without providing any details. There's a vague "sense that there has been some pulling back because of these revelations."
Speaking a press conference Monday, Secretary of State Hillary Clinton said the leak could "create potential dangers for our friends and partners."
In a February 2009 cable, American envoys were asked to identify sensitive places "whose loss could critically impact the public health, economic security, and/or national and homeland security of the United States."
Diplomats responded with a list of installations from all over the world, including a mine located in the Congolese jungle, where cobalt is produced to make jet engines and medical scanners; the largest crude oil processing plant in the world located at Abqaiq, Saudi Arabia; a marine engineering firm in Edinburgh, Scotland "critical" for nuclear submarines; and a Canadian power plant that supplies the northeastern United States.
Clinton said she would not comment on "any specific cable," but said the theft of the cables was "deeply distressing."
Clinton then called on "countries around the world and businesses to assist us in preventing any of the consequences that could either endanger individuals or other interests internationally."
State Department spokesperson P.J. Crowley told ABC News Monday that "for someone to release that kind of information is tantamount to sending a group like al Qaeda a prospective targeting list."
In a statement to ABC News, Hrafnsson said the cables offer additional proof that American diplomats were asked to engage in intelligence gathering, an allegation the State Department denies.