LAS CRUCES, N.M. (AP) — The governor told southern New Mexico residents to keep attending houses of worship after small explosions outside two churches put parishioners on edge.

Gov. Susana Martinez promised that the "coward" will be caught, telling reporters late Sunday that if the intention was to bring fear to those who worship, it was a failed effort.

There were no injuries or deaths from the small blasts just 20 minutes and a few miles apart, but they shocked congregants Sunday morning at the churches in Las Cruces.

Authorities have declined to provide specifics on the explosives, but Las Cruces police spokesman Danny Trujillo said the blasts "had the potential to cause serious injuries if somebody had been nearby."

Calvary Baptist and Holy Cross Roman Catholic received minor damage, he said.

Authorities are working to determine who planted the explosives and have not said if more than one person is being sought. They also are trying to determine what materials were used and whether the blasts were related.

"It doesn't appear to be coincidental because of the timing, but you never know," Trujillo told The Associated Press.

The FBI, the Bureau of Alcohol, Tobacco, Firearms and Explosives and New Mexico State Police are assisting with the investigation.

The FBI has established a hotline, 1-800-225-5324, for information on the blasts.

"Somebody out there knows something, and we want them to call us," FBI spokesman Frank Fisher said.

The first explosive device went off around 8:20 a.m. Sunday in a mailbox on a wall near the administrative entrance to Calvary Baptist. Several worshippers were inside the church at the time, but services had not started, police said.

Churchgoers say the blast shook the building and left debris around the damaged mailbox. Las Cruces police Sgt. Robert Gutierrez described seeing "just a lot of paper shreds."

The next blast came from a trash can outside Holy Cross Catholic around 8:40 a.m. as Monsignor John Anderson was helping pass Communion.

"I was right in the middle of saying the words 'Take and eat, this is my body,' and there was a pow! I mean, I knew it had to be more than a gunshot," Anderson told the Las Cruces Sun-News newspaper (http://bit.ly/1ME7PEp ). "I didn't know if it was a shotgun blast, I didn't know what. But it was very loud, and I just kept on saying the words."

Ann Marie Sullivan, a college student attending Mass, said it "sounded like something had fallen off and shattered the glass in the back."

The trash can was near a glass entryway, which was damaged.

Police arrived and evacuated the church and blocked off surrounding streets. Bomb-sniffing dogs searched the building.

Services were canceled for the rest of the day at both churches, which are less than 4 miles apart. Trujillo said he didn't know of any recent threats against either church.

Other churches in the city contacted police about what, if anything, they should do. Police are advising them to look out for anything suspicious but don't inspect anything themselves.

"Don't go poking around in trash cans or mailboxes," Trujillo told the Sun-News. "If you have any suspicion of anything that's out of the ordinary, please call police and leave it up to the officers to look it over."