SYDNEY (Reuters) - Australian Prime Minister Tony Abbott on Tuesday ruled out an amnesty for Australian citizens seeking to quit foreign militant groups and return home in the wake of media reports that his government was negotiating with potential defectors.

The Australian Broadcasting Corporation reported that the Australian authorities in the Middle East were negotiating with three Australian fighters with the Islamic State in Iraq and Syria radical group who wanted to leave but feared imprisonment at home.

Mr Abbott seemed to confirm their fears on Tuesday, taking a hard line that includes prison time for those who have ignored Australian laws expressly barring them from participating in the conflicts in Syria and Iraq. "If you go abroad to break Australian law, if you go abroad to kill innocent people in the name of misguided fundamentalism and extremism, if you go abroad to become an Islamist killer, well, we are hardly going to welcome you back into this country," Mr Abbott told reporters. "If you go abroad to join a terrorist group and you seek to come back to Australia, you will be arrested, you will be prosecuted and jailed."

Security analysts have put the number of foreign fighters in Iraq and Syria, travelling from scores of countries around the world, in the thousands. Mr Abbott has told Parliament at least 70 Australians were fighting in Iraq and Syria backed by about 100 Australia-based "facilitators".

Australia is on high alert for attacks by radicalised Muslims or by home-grown militants returning from fighting in the Middle East, having raised its threat level to high and undertaken a series of high-profile raids in major cities.

Under tough new security powers won by Mr Abbott's conservative government in October, Australian citizens can face up to a decade in prison for overseas travel to areas declared off limits.