A suspicious package containing unbleached flour arrived at California's Secretary of State's headquarters in Sacramento, what appears to be the latest in a series of suspicious packages sent to election officials across the country, officials reported Thursday afternoon.

In total, suspicious packages were sent to election officials in at least 15 states, officials said. The origin of the Sacramento package is unclear.

“On-site inspection and presumptive chemical testing by state law enforcement determined the substance within the package was harmless and tested positive for unbleached flour,” Secretary of State Shirley Weber said in a statement, adding that federal authorities would continue to investigate the incident.

Weber said he is advising local election offices to take extra precautions before handling any mail that comes into their facilities.

On Tuesday, the FBI and the U.S. Postal Inspection Service began investigating suspicious packages sent to election officials in more than a dozen states, including Alaska, Colorado, Georgia, Indiana, Kentucky, Massachusetts, Missouri, New York, Rhode Island, Mississippi and Connecticut.

So far, there have been no reports of injuries caused by the packages or the hazardous substances they contained, but “unknown substances” have been found in some of the packages, FBI spokeswoman Kristen Cetera said in a statement.

A package delivered to an Oklahoma elections office also contained flour, state officials reported.

This is the second time in recent months that elections offices in multiple states have been targeted by suspicious mail.

According to reports from the FBI and the U.S. Postal Inspection Service, letters were sent to election offices in five states in November, some of which were found to contain fentanyl.

The string of suspicious deliveries comes as early voting begins in several states for the November elections and as former Republican presidential candidate Donald Trump continues to claim without evidence that he lost the last election because of voter fraud, bringing increased scrutiny of the nation's voting process and election officials.

The National Association of Secretaries of State (NASS) released a statement on Tuesday condemning the suspicious mailings and the recent assassination attempt on President Trump.

“There is no place in our democracy for any kind of political violence, intimidation or intimidation,” NASS said.

Weber said the state will continue to work with state and federal law enforcement to monitor any threats against California election workers.

The Associated Press contributed to this report.