WASHINGTON - The State Department has failed to turn over government documents covering Hillary Rodham Clinton's tenure as secretary of state that the Associated Press and others requested under the U.S. Freedom of Information Act ahead of her presumptive presidential campaign. They include one request AP made four years ago and others pending for more than one year.

The agency already has missed deadlines it set for itself to turn over the material.

The State Department denied the AP's requests, and rejected the AP's subsequent appeals, to release the records sought quickly under a provision in the law reserved for journalists requesting federal records about especially newsworthy topics.

In its requests, the AP cited the likely prospect of Clinton entering the 2016 race. The former first lady is widely considered the leading Democratic contender hoping to succeed President Obama. She has made scores of recent high-profile speeches and public appearances.

On Wednesday, the conservative political advocacy group Citizens United sued the State Department for failing to disclose flight records showing who accompanied Clinton on overseas trips.

Citizens United, which in 2009 mounted a legal battle that led to the landmark U.S. Supreme Court decision overturning campaign finance limits, said the department unlawfully was withholding the records it sought nearly five months ago.

The State Department is among the U.S. government's worst-performing federal agencies under the Freedom of Information Act. There is no direct evidence that political considerations in a Democratic presidential administration have delayed the release of files about the party's leading contender for 2016. But the agency's delays, unusual even by government standards, have stoked perceptions about what could be taking so long.

"There may not necessarily be political interference, but if the department went out of its way to speed these documents there would be no way for people to accuse them of it," said Thomas Blanton, who has previously sued the State Department for access to records as director of George Washington University's National Security Archive, a research organization.

The department "is stonewalling us," said Citizen United's president, David Bossie.