Chase banks in Oklahoma -- including one in Norman -- were back to business as usual Tuesday, after receiving threatening letters containing a powder substance the day before.

Meanwhile, more threatening letters containing the powder were received Tuesday at nine banks in New Jersey and a credit card center in Illinois, officials said.

In all, about 30 letters containing the suspicious powder have been mailed to Chase banks in seven cities around the country.

An FBI spokesman said preliminary assessments have determined the powder to be harmless. FBI spokesman Gary Johnson said although field tests have been negative, "additional testing will be conducted."

All the Chase branches in Oklahoma are open today and conducting "business as usual," JP Morgan Chase spokesman Greg Hassell said Tuesday.

"We've received suspicious mail in another nine locations in New Jersey and two at a credit card center in Elgin, Ill.," Hassell said. Elgin is about 30 miles northwest of Chicago.

The Chase bank at 3600 W. Robinson St. was closed late Monday morning after an employee opened a piece of mail threatening the release of a hazardous material.

Officials said eight notes were sent to Chase branches in the Oklahoma City metro area -- four in Oklahoma City, one in Norman, one in Edmond and one in Yukon. One of the letters was intercepted by the postal service, officials said.

Although many of the letters "have contained a white powder," Hassell said it's "important to point out that all the suspicious mail that's been tested has turned out to be harmless."

Hassell said the "threatening letters have similarities," but that he's not familiar with the contents of all the letters.

Johnson said the FBI, the U.S. Postal Inspection Service and state and local authorities are investigating the letters.

Johnson warned that "even sending a hoax letter is a serious crime."

"Anyone with information is requested to contact the FBI, the U.S. Postal Inspection Service and state and local authorities," he said.

Anyone with information can "also go to www.fbi.gov to submit a tip," Johnson said.

"As the investigation is an ongoing matter, we cannot discuss further matters at this time," he said.