AUSTIN, TEXAS — Residents of a southwest Austin neighborhood were told to stay inside early Monday after a fourth explosion in less than a month hit Texas’ capital, injuring two men and stoking fears in a city already on edge.

The latest blast occurred Sunday just after 8:30 p.m. local time (9:30 p.m. ET). Two bicyclists who are believed to be in their 20s sustained injuries that were not life-threatening, officials said.

The two men came across a suspicious device on the side of the road, Austin Police Chief Brian Manley said during a late-night news conference.

Unlike the prior explosions, the one Sunday may have been triggered by a tripwire, according to Manley.

“We will not be able to send school buses into the neighborhood on Monday,” he said. “In addition to that, we’re going to ask the residents in the Travis County neighborhood to stay in your homes tomorrow morning and give us the opportunity to process the scene once the sun comes up.”

He asked those in the neighborhood to stay inside until 10 a.m. (11 a.m. ET).

Manley also asked the community “to have an extra level of vigilance and pay attention to any suspicious device, whether it be a package, a bag, a backpack, anything that looks out of place and do not approach it.”

Police are working under the belief that the incident Sunday is related to a string of unsolved package bombings this month that killed two and injured two others, though a link has not yet been confirmed.

They also are examining whether the packages have been specifically meant to target minorities. Stephen House, 39, was killed on the morning of March 2, and Draylen Mason, 17, died on the morning of March 12. Both were black members of the same church, Nelson Linder, the local NAACP chapter president, told NBC News last week.

Source: NBC News