An AWOL soldier who had weapons stashed in a motel room near Fort Hood has admitted to planning an attack on the Texas post, where 13 people died in 2009 in the worst mass shooting ever on a U.S. military installation, the Army said in an alert issued Thursday.

Pfc. Naser Abdo, a 21-year-old soldier who was granted conscientious objector status this year after he said his Muslim beliefs prevented him from fighting, was arrested Wednesday. Agents found firearms and "items that could be identified as bomb-making components, including gunpowder," in his motel room, according to FBI spokesman Erik Vasys.

The Army alert sent via email and obtained by The Associated Press says Abdo was arrested by Killeen police after a tip from the owners of a gun shop and "was in possession of a large quantity of ammunition, weapons and a bomb inside a backpack." Upon questioning, the alert says, he admitted to planning an attack on Fort Hood.

Officials have not offered details about Abdo's possible intentions. The infantry soldier from Fort Campbell, Ky., whose hometown is Garland, Texas, had applied for conscientious objector status last year. A military review board recommended this spring that he be separated from the Army.

But the discharge was delayed after Abdo was charged with possessing child pornography. Fort Campbell civilian spokesman Bob Jenkins said Abdo "was fully aware that he was being investigated for possessing child pornography since November 2010." An Article 32 military hearing last month recommended he be court-martialed; he went absent without leave during the July 4 weekend.

The military's criminal investigation division, along with the federal Joint Terrorism Task Force, also had investigated Abdo earlier this year after he was flagged for making unspecified anti-American comments while taking a language class in April, according to a U.S. official briefed on the investigation.

The official, who spoke on condition of anonymity because the investigation is ongoing, said neither the military nor the task force discovered anything at the time to indicate Abdo was planning an attack, the official said.

Abdo's arrest came after the owners of a local gun store _ the same store where the 2009 Fort Hood shootings suspect Maj. Nidal Hasan bought a pistol used in the attack _ called police, the Army's alert said.

Store clerk Greg Ebert said the man arrived at Guns Galore LLC by taxi Tuesday and bought 6 pounds of smokeless gunpowder, three boxes of shotgun ammunition and a magazine for a semi-automatic pistol, paying about $250. Ebert said he became concerned when the man asked questions indicating he didn't know much about the items.

"(We) felt uncomfortable with his overall demeanor and the fact he didn't know what the hell he was buying," Ebert said. "I thought it prudent to contact the local authorities, which I did."

Killeen police learned from the taxi company that Abdo had been picked up from a local motel and that he also had visited an Army surplus store where he paid cash for a uniform bearing Fort Hood unit patches, according to the Army alert.

Vasys said the FBI would charge Abdo with possessing bomb-making components and he would be transferred from Killeen police into federal custody. Vasys said there was nothing to indicate Abdo was "working with others."

An Oklahoma attorney who has represented Abdo said Thursday he hadn't heard from Abdo in weeks and learned of the arrest from a Texas television station.

"I've been quite anxious to get in touch with him," said attorney James Branum.

Hasan, an Army psychiatrist, faces a possible death sentence when he is tried next year on 13 counts of premeditated murder and 32 counts of attempted premeditated murder in the 2009 rampage at Fort Hood.

The Army post issued a statement seeking to reassure the community after Abdo's arrest Thursday.

"At this time, there has been no incident at Fort Hood," the statement said. "We continue our diligence in keeping our force protection at appropriate levels."

Fort Campbell spokesman Rick Rzepka referred all questions to the Pentagon.

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Associated Press writers Diana Heidgerd in Dallas, Pauline Jelinek and Eileen Sullivan in Washington, and Janet Cappiello in Louisville, Ky., contributed to this report.