A Yahoo transparency report released Thursday showed that the United States topped the list of countries demanding information about users in the first half of this year.

The United States called on the California-based Internet veteran to disclose data from accounts of 12,533 users, compared with the 4,759 accounts targeted by second-place Taiwan, according to the report.

Data was only provided in a fraction of the cases, Yahoo reported.

"We've worked hard over the years to earn our users' trust and we fight hard to preserve it," Yahoo chief executive Marissa Mayer said in an introduction to the report.

The transparency report included requests made with National Security Letters cloaked in secrecy, and which come with a six-month reporting delay imposed by the US government.

"On the international front, a number of countries seek to expand their surveillance authorities beyond their borders," Yahoo general counsel Ron Bell said in the report.

Bell maintained that US Department of Justice efforts to improve a Mutual Legal Assistance Treaty process could help counter the "worrisome trend."

"We will continue our efforts to protect your information from unclear, improper, overbroad or unlawful government requests," Bell said.

More than 800 million people around the world visit Yahoo daily in online "habits" including tending to email, sharing photos, and tracking news or sports, according to the company.

Court documents disclosed earlier this month showed that US authorities threatened to fine Yahoo $250,000 a day if it failed to comply with a secret surveillance program requiring it to hand over user data in the name of national security.

The documents, made public in a rare unsealing by a secretive court panel, "underscore how we had to fight every step of the way to challenge the US government's surveillance efforts," Bell said in a blog post at the time.

US online snooping

The documents shed new light on the Prism snooping program revealed in leaked files from former National Security Agency contractor Edward Snowden.

The program allowed US intelligence services to sweep up massive amounts of data from major Internet firms including Yahoo and Google. Officials have said the deeply contentious program ended in 2011.

The 1,500 pages of documents were ordered released by the Foreign Intelligence Surveillance Court in the case dating from 2007, according to Bell.

"We refused to comply with what we viewed as unconstitutional and overbroad surveillance and challenged the US government's authority," he said.

Yahoo's court challenge failed and it was forced to hand over the US user data.

"At one point, the US government threatened the imposition of $250,000 in fines per day if we refused to comply," Bell revealed.

Since the Snowden leaks, Yahoo and others have been seeking to make public these court documents to show they were forced to comply with government requests and made numerous attempts to fight these efforts, rather than simply acquiescing to them, as some critics say.

The redacted court records, seen by AFP, showed Yahoo challenged the government on constitutional grounds, saying the surveillance program violated protections against unreasonable search and seizure.

"The US Supreme Court has never sanctioned warrantless surveillance of US citizens," Yahoo said in a legal brief.