Six nationals of the former Yugoslavia were arrested on charges they plotted to attack the Fort Dix Army base , federal authorities said Tuesday.

The six were scheduled to appear in US District Court in Camden later Tuesday to face charges of conspiracy to kill US servicemen, said Michael Drewniak, a spokesman for the US Attorney's Office in New Jersey.

Five of them lived in Cherry Hill, about 10 miles east of Philadelphia and 20 miles southwest of Fort Dix, he said.

A law enforcement official, speaking on condition of anonymity because documents in the case remain sealed, said the attack was stopped in the planning stages.

The men were arrested while trying to buy automatic weapons in a sale set-up by law enforcement authorities, the official said. Authorities believe the men trained for the attack in the Poconos and allegedly conducted surveillance at other area military institutions, including the Army's Fort Monmouth, the official said.

The official said that the men had lived in the United States for some time and were arrested as part of a joint federal and local investigation.

The Star-Ledger of Newark reported on its Web site that the men had agreed to buy AK-47 assault rifles from an arms dealer who was secretly cooperating with the FBI. It cited a law enforcement person who spoke on condition of anonymity because the source was not authorized to speak about the arrests.

FBI spokeswoman Jerri Williams said US Attorney Christopher Christie and J.P. Weis, special agent in charge of the FBI in Philadelphia, planned a 2:30 p.m. news conference to discuss the arrests.

Fort Dix is used to train soldiers, particularly reservists. It also housed refugees from Kosovo in 1999.