DENVER ” White powder accompanied by threatening notes prompted evacuations at three downtown buildings housing state agencies Monday, while a powdery substance at a suburban building forced the evacuation of a state police call center.

The substances in all four cases turned out to be harmless, authorities said.

“I know there were several incidents _ whether they were all connected or isolated, I’m sure there will be a thorough investigation,” said trooper Eric Wynn, a spokesman for the state patrol, which is investigating the incidents.

An envelope sent to the state Department of Natural Resources near the State Capitol contained sugar and one sent to the World Trade Center contained a sugar substitute, Fire Department spokesman Phil Champagne said. Another envelope sent to the building housing the Department of Regulatory Agencies, or DORA, also contained a sugar substitute, he said.

The Natural Resources building was evacuated shortly before 1 p.m. and three floors of the World Trade Center were evacuated shortly after 1, Champagne said. The World Trade Center also houses some state workers but it was not immediately clear if the substance was sent to any of them. The letter sent to DORA was discovered at about 5 p.m.

In Lakewood, about 7 miles west of downtown Denver, an employee opening a letter sent to the state Department of Agriculture came into contact with a powder, forcing the evacuation of the four-story building that houses several state agencies, including the state patrol’s Denver dispatch center, Wynn said.

The employee was decontaminated as a precaution.

State Patrol spokesman Lance Clem said at least one of the envelopes had information that will make it “interesting and easy to investigate,” but he did not elaborate.

Champagne said two Monday incidents appeared to be related but investigators don’t believe there is any connection to an incident on Sunday, when workers at a Denver bank found five capsules containing a yellow powder in an envelope.

Initial tests indicated the powder was a protein and not anthrax, authorities said.

Bank employees, who were processing commercial bill payments, were scrubbed down in a decontamination tent. No injuries were reported.