Philadelphia police are investigating a threat made against three police districts in the city.

The department released a statement Monday night saying police are taking the threat "seriously," and that it will be "thoroughly investigated."

The department did not elaborate on the circumstances surrounding the threat, but WPVI-TV reports a person alerted an officer about a threatening message on Facebook. The message said that someone would blow up three district buildings with a bomb.

Police have been on high alert since a gunman shot and killed five police officers in Dallas during a protest last week over recent fatal shootings by police.