Libby was sentenced to two-and-a-half years in jail

Libby was convicted for perjury and obstruction of justice in a probe into the leaking of the identity of CIA officer Valerie Plame.

A former chief of staff to Vice-President Dick Cheney, Libby was the only person charged in the case.

US President George W Bush commuted Libby's 30-month prison term earlier this year.

Libby was still ordered to serve two years of probation and pay a $250,000 (£123,000) fine.

Tactical

"We remain firmly convinced of Mr Libby's innocence," the former aide's lawyer Theodore Wells said.

"However, the realities were that after five years of government service by Mr Libby and several years of defending against this case, the burden on Mr Libby and his young family of continuing to pursue his complete vindication are too great to ask them to bear."

WHAT IS CIA LEAK CASE ABOUT? Libby was found guilty of lying to the FBI and a grand jury over revelations about CIA agent Valerie Plame's identity Critics said the White House leaked Ms Plame's identity to undermine her husband, ex-ambassador Joseph Wilson He had publicly cast doubt on the Bush administration's case for war in Iraq The alleged cover-up, rather than the leak itself, was the subject of the Libby trial

Q&A: CIA leak case

The decision to drop the appeal is also a tactical one, correspondents say.

Even if a federal appeals court overturned Libby's conviction, that would lead to another long and costly trial.

If he was convicted again, Mr Bush's commutation would not apply and the president is likely to have left office.

Mr Bush has not ruled out a full pardon for Libby.

No-one was charged with the leaking of Ms Plame's identity.

Ms Plame alleges that the leak was politically motivated. Her husband had criticised the Bush administration's decision to go to war in Iraq.