Armed men opened fire at a wedding ceremony in northern Afghanistan, killing at least 21 guests and wounding eight, provincial officials said on Monday.
Violence has increased sharply this year in most parts of Afghanistan, after U.S.-led forces formally ended their combat mission at the end of 2014, leaving a small contingent of about 12,000 NATO troops to train Afghan forces.
It was not immediately clear what prompted the attack in the northern province of Baghlan, but insurgent activity has increased in the province over the past year and private militias have proliferated.
"There was a wedding party, which turned to a tragedy, after some armed men entered and opened fire on male guests," Baghlan police chief General Abdul Jabar Pordeli told Reuters by telephone.
"An investigation is ongoing and police will arrest all perpetrators," added the police chief.
Around 2,500 armed members of illegal groups operate in Deh Salah district, where the attack took place, said district police chief Color Gulestan.
Civilian casualties have risen 16 percent in the first four months of 2015, according to the United Nations, which recorded a total of 2,937 civilian casualties over the period.
More the 10,000 Afghan civilians were either killed or injured last year, U.N. figures show, the most violent year since it began tracking numbers in 2009.
Weddings in rural Afghanistan start in the evening and parties follow a custom of keeping men and women guests apart.