Whatever breached security at Pine Bluff Arsenal late Tuesday night wasn’t human, officials said Thursday.

A day after reporting that a guard had spotted three unidentified intruders near a stockpile of deadly chemical weapons, arsenal officials said they had found no tracks or other evidence of human intrusion and that the uninvited guests could have been animals.

“The security guard reported he definitely saw something. He stands by his report,” spokesman Cheryl Avery said.

Dogs from Little Rock Air Force Base and law enforcement officers did a thorough sweep of the Bond Road Exclusion Area, where the breach was reported shortly before midnight Tuesday. The 500-acre area is in the northern part of the arsenal where chemical weapons are stored. No evidence of human intrusion was found in the area, which is restricted to authorized personnel.

“The security and safety of the stockpile was never at risk,” Col. Brian S. Lindamood, the commander of the installation, said Thursday in a statement. He said the installation’s security procedures operated effectively “with no notice and in short order.”

The guard who made the report will not be disciplined, Avery said. “The officer who made the initial report was commended for the promptness of his report, for the detail contained in his report and for his diligence in following up,” Avery said. “He performed exactly as he’d been trained.”

Security was tightened Wednesday with all vehicles entering and leaving the arsenal being searched.

Avery said she couldn’t speculate whether the guard saw animals. No animal tracks were spotted, but the officers conducting a sweep were looking for evidence of humans, not wildlife. Some of the installation is wooded.

U.S. Rep. Mike Ross, D-Ark., told the Associated Press on Thursday that he wasn’t disturbed by the report of intruders.

“We’ve had people scale the fence at the White House, which consists of a few acres,” said Ross, who represents Pine Bluff.

“We’re talking about an area here that consists of 13,000 acres.”

The arsenal, one of eight sites where the nation stores chemical weapons, holds 12 percent of the United States’ chemical weapons stockpile. Incineration of chemical weapons, which began March 29, is on hold until May because of a maintenance project.

For decades, weapons containing nerve gas and chemical agents such as mustard gas have been stored in underground igloos at the arsenal. The United States is working to destroy its national stockpile by 2012 to comply with an international treaty.

This story was published Thursday, January 26, 2006.