The Federal Bureau of Investigation seal is seen at FBI headquarters in Washington
The Federal Bureau of Investigation seal is seen at FBI headquarters in Washington, U.S. June 14, 2018.

The number of murders reported in the United States rose last year, the FBI said on Wednesday, but it warned that a change in its data collection methods meant that its tally excluded the nation's two largest cities, New York and Los Angeles.

The bureau said its data suggested that the number of murders reported in the United States rose by 4.3% since 2020.

Justice Department officials told journalists on a Tuesday conference call ahead of the full data set's release that a transition to a new method of data collection meant that just 52% of U.S. law enforcement agencies had submitted their full 12-month 2021 crime data by the bureau's March 2022 deadline.

The data does not include full reports from agencies including the New York City Police Department, the Los Angeles Police Department, the Los Angeles County Sheriff's Office, the San Francisco Police Department and the Phoenix Police Department.

The increase, and the incomplete data, could draw criticism as Republicans increasingly focus their campaign messaging on concerns about crime ahead of the November midterm elections, when they are favored to win back control of at least one chamber of Congress from President Joe Biden's Democrats.

A Reuters/Ipsos poll published on Wednesday, showed that registered voters, including the key demographic group of suburban women, believe that Republicans are better suited to addressing crime than Democrats.

This marks the first time the FBI and the Justice Department's Bureau of Justice Statistics have fully transitioned to a more detailed crime-reporting system, known as the National Incident-Based Reporting System.

About 9,700 law enforcement agencies were not able to supply full data sets by the March 2022 deadline for Wednesday's report.

Justice Department officials said some of the new data released on Wednesday will include estimates that were developed based on partial-year data reported by some of the law enforcement agencies. Department officials said they were able to generate state-level estimates for about 40 of the 50 the states, which covers about 65% of the U.S. population.

Justice Department and FBI officials told reporters on Tuesday that the new methodology for crime data collection will include many new details on crimes that previously went unreported. These include data for drug offenses, human trafficking numbers, bribery, counterfeiting, and more detail on things such as simple assault and intimidation offenses.