A dozen people were robbed in separate confrontations around Minneapolis — nine of them on Monday alone — over a roughly 36-hour period between Sunday afternoon and Tuesday morning, authorities said.

The armed stickups were the latest in a wave of violent events since the beginning of the year, which has seen serious crimes like robbery and aggravated assault increase 8 percent citywide, compared to this time last year, according to police statistics. The department hasn’t offered any explanation for the recent spike and an e-mail for a spokesman wasn’t immediately returned on Tuesday afternoon.

The incidents ranged from a robbery victim who was left bloodied and bruised after being accosted by 12 suspects a few blocks from Third Precinct police headquarters to a 44-year-old man who was relieved of $500 at gunpoint in broad daylight. Seven of the robberies occurred in south Minneapolis. Two involved vehicles, with officers responding to a reported carjacking in the 3200 block of Washington Avenue N. In another case, a man and woman were held up in the early morning hours of Monday by two male suspects, one of whom was holding a gun, near the corner of 34th Street and Minnehaha Avenue S., according to an police incident report. The thieves reportedly made off with the keys to the man’s rental car.

Only one of the incidents ended in an arrest, after a victim provided police with a description of the two people — one, an 18-year-old man; the other, a juvenile — who robbed him at gunpoint inside an apartment building in the 3000 block of Pillsbury Avenue S.

Department statistics show that citywide, the number of robberies so far this year has risen nearly nine percent, compared to the first three-and-a-half months of 2015. The Second and Third police precincts have seen the sharpest increases in such crimes. In the Second Precinct, which covers parts of south Minneapolis, the number has nearly doubled, to 51 through April 11, the last date for which reliable data are available.

Although criminologists caution against reading too much into early-month numbers, the crime surge hasn’t escaped notice by residents in some of the city’s hardest hit neighborhoods.

The incidents:

• On April 12, at 5:06 a.m., a 42-year-old man was punched several times in the face and had his belongings stolen. He was taken to HCMC, from 3020 Pillsbury Av. S.

• On April 11, at 10:30 p.m., at 24th Street and Chicago Avenue S., officers responded to 3200 Washington Av. N. for a carjacking of a 27-year-old man.

• On April 11, at 10:18 p.m., at 1506 E. 23rd St., a 54-year-old woman was robbed at knifepoint. She refused medical attention.

• On April 11, at 9 p.m. at 3101 2nd Av. S., 26-year-old man was robbed by two suspects, one of whom flashed a handgun and demanded money, and then cut him with a broken beer glass bottle. He was treated at the scene.

• On April 11, at 6 p.m. at 58th St. and Bossen Terrace, a 26-year-old man was robbed by 12 suspects, who took his iPhone and wallet. He suffered swelling and bleeding to his face and was taken to HCMC.

• On April 11, at 2:15 p.m., a 46-year-old man had the two suspects in his apartment, when one of the suspects demanded his money and he refused and a fight broke out. One of the men held him down as the other cut him in the side and face with a box cutter. They then left, taking some items from his bed.

• On April 11, at 2:35 a.m., at 34th Street and Minnehaha Avenue S., a 49-year-old man and a woman were robbed at gunpoint by two unidentified men. They took the keys to the rental car he was driving.

• On April 11, at 2 a.m., at the corner of Quincy St. and Lowry Avenue NE., a 42-year-old man was robbed and received minor injuries, but refused medical attention.

• On April 11, at 1:30 a.m. at 1510 Logan Av. N., a 31-year-old woman was robbed. She was not injured and was unable to provide a suspect description.

• On April 11, at 11:40 p.m. on April 10, at 3018 Pillsbury Av. S., Apt. 303, an 18-year-old and a juvenile robbed someone at gunpoint, who provided officers with suspect descriptions that led to their arrests.

• On April 10, at 3:30 p.m., officers responded to a robbery at the corner of W. Broadway and Lyndale Avenue N. The victim a 44-year-old man, said he was robbed at gunpoint by two unknown suspects and had $500 taken, but wasn’t harmed.

Libor Jany • 612-673-4064 Twitter:@StribJany