Preliminary testing has shown the white powder is not toxic.
9News.com says nine banks, yet ABC7 News says it is ten banks in the two states.
Some of the banks were closed and evacuated as police and Hazmat crews were called in to investigate and decontaminate.
The Chase Bank in Arapahoe County was inside an Albertson's grocery store. After a suspicious package was found at that bank, the entire store was evacuated, police said.
In Oklahoma, two Chase bank branches in Oklahoma City and one in Norman, Okla., also received threatening letters with white powder, the FBI said.
FBI spokeswoman Kathy Wright in Denver said investigators believe the incidents are related.
Mary Jane Rogers, a spokeswoman for JP Morgan Chase & Co. in Phoenix, said bank officials are cooperating with the FBI and local police in both states.
The bank released the following statement: "Several branches in Colorado and Oklahoma received threatening letters, some with suspicious powder. The branches are in Metro Denver, Oklahoma City and Norman, Oklahoma areas. There are no reported injuries but some employees did request to be examined by a doctor. We take these threats seriously and are working closely with law enforcement."
All of the banks that were sent the letters were Chase Bank branches.
No one has been taken to the hospital according to Mary Jane Rogers, JP Morgan Chase spokesperson. She says some bank locations were evacuated, but did not have an exact number.
The FBI has also confirmed it has responded to two Chase Bank locations in Denver, and one each in Centennial, Westminster, Lakewood and Arvada. The FBI says all banks were closed for decontamination as a precaution.
Two banks in Oklahoma City also recieved the letters and another in Norman, Okla. also got a letter.
Denver Fire Department confirmed to 9NEWS that one of the affected banks is the Chase Bank located near Martin Luther King Blvd. and Colorado Blvd.
Denver Fire says an employee at that branch found the powder when he opened a letter.
In Westminster, an employee at the branch near 94th and Sheridan opened a letter just before 2 p.m. on Monday. The Westminster Fire Department says 17 people were held while a Hazmat team tested the powder. A test revealed it was harmless and they were released. The FBI took a sample of the substance.
In Arvada, the fire department says the letter was sent to the branch at 80th and Kipling. They determined it was a type of calcium powder and was not hazardous.
The West Metro Fire Department says they responded to a bank at Colorado Mills Mall.
The Cunningham Fire Department says they responded to a bank at Smoky Hill and Buckley just after 1 p.m. The powder there was determined to be not hazardous and the crews left the scene by 4 p.m.
Lutheran Hospital says its emergency room went into lockdown temporarily on Monday afternoon after two people from one of the banks were taken there to get checked out. The lockdown was standard procedure and only lasted for about 35 minutes while the two people were decontaminated.
Rogers says in addition to working with the FBI, JP Morgan Chase is also working with U.S. Postal Inspection Services.
More at Reuters but I am not seeing anything about the language of what is being called the "threatening" letters.
Rogers said Chase would not release the total number of banks affected until they were sure all the letters had been found.
"We immediately called the FBI and Postal Inspection Service to handle the matter and ensure the safety of our customers and employees," Rogers said.
She did not know the contents of the letters or if they contained return addresses.
At least it was a false alarm but shutting down banks like this is definitely worrisome especially with the number of banks this happened to.
6 of the banks and locations have been released as:
Denver -- 3300 Colorado Blvd.
Denver -- 1760 16th St.
Lakewood -- 1400 W. Colfax
Arvada -- 8015 Kipling St.
Arapahoe County -- 16746 E. Smoky Hill Road
Westminster -- 94th and Sheridan