OPPOSITION Leader Tony Abbott believes it's likely Kevin Rudd will make a move on Prime Minister Julia Gillard soon.

Mr Rudd, who flew out of Australia for a security conference in Germany late on Thursday, has said several times this week he is happy with his role as foreign minister.

"I am delighted to be the foreign minister of this country and I am delighted to be out there working on Australia's behalf," he said.

But speculation has been swirling that Ms Gillard may be under threat from Mr Rudd, whom she ousted in a leadership coup in 2010, and the opposition is seizing on the unrest.

"Look, all the signs are there. It is a very, very restless caucus," Mr Abbott said.

"In the end it's up to the Labor Party to choose which failed leader it wants to take into the election."

Mr Abbott said he expected Mr Rudd to make the move before the March 24 Queensland election campaign gets into full swing.

"My instinct is he'll make a move before the Queensland election because if Kevin is such a miracle worker in Queensland you'd think they'd want him there before the state election."