The White House renewed an appeal on Tuesday for information on the location of a US journalist abducted in Syria 1,001 days ago.

"This week, it is with a heavy heart that we mark American journalist Austin Tice's 1,000th day in captivity," said National Security Council spokeswoman Bernadette Meehan.

"We strongly urge Austin's captors to release him so that he can be safely reunited with his family."

"We call on all those who may have information about Austin’s whereabouts – governments and individuals – to work cooperatively with us to help bring him home."

The Marine Corps veteran was abducted near Damascus on August 14, 2012.

He is not believed to be held by the extremist Islamic State group.

His father Marc Tice has said the circumstances of his son's captivity "are still to a large degree a mystery to us" but information suggests he is held by "a Syrian entity of one type or other."

Austin, a freelance journalist working for McClatchy News, the Washington Post, CBS and others, has been honored with the George Polk Award for War Reporting and the McClatchy President's Award.

He has also worked for AFP, the BBC and Associated Press.

His family have at times been critical of the way the White House has handled his case, saying communication with the Obama administration has been poor.

The White House is currently reviewing how it deals with hostage situations abroad.