Police in Austin, Texas, have urged residents to stay indoors following a series of explosions in the area, The Associated Press reported.

The latest blast, the fourth in recent weeks, occurred Sunday night and left two people wounded.

“We now need the community to have an extra level of vigilance and pay attention to any suspicious device,” said Austin Police Chief Brian Manley, according to Reuters.

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“Given that there may have been a different triggering mechanism in this device, we wanted to get that out as early as possible.”

Two people were killed earlier this month during three package explosions in three different Austin neighborhoods.

Officials were also probing whether or not the first three explosions qualified as hate crimes. The two individuals killed were African-American men, while a Hispanic woman was wounded.

The fourth bomb may have been ignited using a tripwire, while the other three blasts went off when packages were touched, according to Manley.

“We’re working on the belief that they are connected,” the police chief said of the several bombings.