Groups promoting Islamic extremism have gained a foothold in US prisons, and counter-terrorism officials believe al-Qaeda is likely to try to use the jails "to radicalise and recruit inmates," a Justice Department investigation reportedly found.

The report from the Justice Department Inspector General's office, investigators said safeguards were so loose in the 105 federal prisons that inmate chapels "remain vulnerable to infiltration by religious extremists," The New York Times said.

The investigation, the paper said, grew out of concerns among members of US Congress that groups training Muslim chaplains had terrorist ties and were breeding extremism. But the investigation found that the problem of "radicalised" prayer sessions was less a reflection of the chaplains than of unsupervised inmates who were allowed to lead their own worship meetings.

"Too many opportunities for abuse... exist," the report found.

The Inspector General's report, the first detailed look into how the federal prisons have dealt with extremist beliefs since the September 11 attacks, is likely to upset Muslim leaders, who say they have been subjected to unfair scrutiny and criticism because of their religious beliefs, the Times said.

Several groups that have trained Muslim chaplains have vigorously denied charges of terrorist links, and Muslim leaders point out that charges against a military chaplain at Guantanamo Bay accused of aiding terrorism collapsed, the paper said.

The Inspector General concluded that while the problem of terrorist recruitment in the federal prisons was not necessarily widespread, officials needed a number of systemwide improvements to ensure tighter control.

Prison officials were quoted as saying Tuesday that they had already moved to fix some problems identified in the report by demanding more information about outside groups that train chaplains and by improving communications with the Federal Bureau of Investigation.