Ottawa ? On a day many devoted to remembering the victims of the 9-11 terrorist attacks, people here were reminded why the country was on high alert for the tragedy’s one-year anniversary.

An anthrax scare closed the Ottawa post office and halted mail deliveries as local and U.S. Postal Service authorities investigated the potential threat.

Police investigate at the Ottawa Post Office after an unmarked envelope was found containing a suspicious white powder. Preliminary anthrax tests came back negative Wednesday afternoon, but results can't be confirmed for 48 hours.

By Wednesday afternoon, preliminary tests on a powdery substance found with an unmarked envelope on the post office floor had returned negative for anthrax, but the building remained locked.

“Especially given the significance of today, we’re taking every precaution for the safety of our employees and our customers,” said Postal Inspector Tom Rebottaro with the U.S. Postal Inspection Service in Kansas City, Mo.

The enveloped was not addressed or postmarked and contained no written threat, Rebottaro said. A post office employee discovered it along with the powdery substance inside it and around it on the floor in a nonpublic area of the building, he said.

The post office, at 401 S. Hickory St. in downtown Ottawa, had not yet opened to the public when the envelope was discovered, shortly before 7 a.m. The post office usually starts the day with 29 employees, but it’s unclear whether they all were in the building when it was evacuated Wednesday morning, said Terry Penland, customer relations manager for the Postal Service’s Mid-America District.

Ottawa postal workers did not deliver mail on Wednesday, and a Franklin County Health Department spokeswoman said a decision on when to reopen the post office would not be made until today.

A note taped to the building’s west entrance informed customers that the post office was temporarily closed.

¢ White powdery substance shuts down Ottawa post office

Still, a steady stream of afternoon customers tried the north doors with no luck. Some wondered aloud if they had missed an announcement that Sept. 11 had been declared a national holiday.

Customer Linda Seitz wasn’t all that surprised to find out why the post office was really closed.

“There’s lots of crazy people in the world,” she said.

Although she figured the envelope and powder were just part of a hoax, she said she was glad authorities were checking to make sure.

“I did tell my grandchildren when they get their mail tomorrow to wash their hands real good,” she said. “You never know.”

Kansas Department of Health and Environment spokeswoman Sharon Watson said the negative anthrax results from Wednesday’s preliminary tests could not be confirmed for 48 hours.

In the meantime, Ottawa Police continue their investigation.

We’re “trying to find out where the envelope came from,” Capt. Ron Puterbaugh said.

In the wake of the Sept. 11, 2001, terrorist hijackings, anthrax letter attacks across the Eastern Seaboard left five dead and at least 13 others ill. The Bush administration on Tuesday raised the nation’s level of terrorist threat to “high” and urged Americans to be on alert for suspicious activity.

Ernest Mustain Sr., who dropped by the post office Wednesday afternoon to check his mail and buy stamps, said the incident hoax or not made him uneasy.

“It’s sad that people have to go to that extreme,” he said. “I hope and pray it’s just a prank.”