Visitors to the site found that Twitter's homepage had been replaced by a page showing a green flag under red text reading "This site has been hacked by Iranian Cyber Army."
The website's official blog acknowledged the disruption on Friday, but gave no details as to how the site had been been hacked and who had carried out the attack.
Biz Stone, the site’s co-founder, wrote on the blog: "As we tweeted a bit ago, Twitter's DNS [Domain Name Service] records were temporarily compromised tonight but have now been fixed."
"We will update with more information and details once we've investigated more fully," he said.
Technology blogs including TechCrunch said Twitter went down around 06:00 GMT for about an hour.
Screengrabs posted on the Flickr photosharing site showed text on the Iranian Cyber Army's replacement page which seemed to criticise reported efforts by the US state department to influence Twitter to postpone maintenance work during recent protests against the Tehran government.
"USA think they controlling and managing internet by their access [sic], but they don't, we control and manage internet by our power," the text said.
"Now which country in embargo list? Iran? USA? We push them in embargo list. Take care," it read.
Iranian demonstrators protesting against the results of June presidential elections used Twitter extensively, both to organise marches and to release information about their movement.
Their use of the microblogging site led some to dub the action against Mahmoud Ahmadinejad, the re-elected Iranian president, a "Twitter revolution" and made the Iranian election one of the top "trends" on the site this year.
TechCrunch reported that the disruption also affected Google searches for Twitter.
It posted a screengrab showing that searches for a time returned a result reading "This website has been hacked by Iranian Cyber Army," it said.
TechCrunch translated the text as saying that it was a reaction to Twitter's interference in the internal affairs of "my country", which it said the US authorities had ordered.
The Iranian authorities repeatedly criticised the US and its allies for "interfering" in the country's internal affairs as the mass protests took place following the disputed election.