Yahoo said U.S. law enforcement agencies made between 12,000 and 13,000 requests for data in the last six months, the latest in a series of disclosures by technology companies since intelligence leaks showed the extent of government data gathering efforts.
The company said the requests were made between December 1, 2012 and May 31 this year.
"The most common of these requests concerned fraud, homicides, kidnappings, and other criminal investigations," Yahoo said in a statement posted on its Tumblr page.
Others were made under the U.S. Foreign Intelligence Surveillance Act, it said.
Technology companies have been under pressure to disclose the precise nature of their cooperation with the U.S. National Security Agency (NSA) after leaked documents showed it had been acquiring consumer data from them for years.
Edward Snowden, a disillusioned former CIA computer technician who had worked as a contractor at the NSA, identified himself as the source of multiple disclosures on the surveillance that were published by the Guardian and the Washington Post this month.