The attack occurred during Friday prayers at the Sayed Abad mosque in Kunduz, provincial spokesman Matiullah Rohani told CNN.
Friday's mosque bombing "is part of a disturbing pattern of violence" and the third deadly attack this week "apparently targeting a religious institution," the UN mission in Afghanistan (UNAMA) said on Twitter.
The bombing comes days after another mosque was targeted in central Kabul, killing at least seven people. That attack on Monday targeted the gates of the Eidgah Mosque in the Afghan capital, where a funeral service was being held for the mother of Taliban spokesman Muhajid.
The Islamic State affiliate IS Khorasan (ISIS-K) claimed responsibility for Monday's bombing, one of a series of attacks the terror group has launched since the Taliban seized control of Afghanistan more than a month ago. Others include a suicide attack at Kabul's airport in August and a spate of bombings targeting members of the Taliban in the eastern Afghan city of Jalalabad.
The group poses a threat to the country's stability and the Taliban's rule. In recent days, the Taliban conducted several operations targeting ISIS-K militants.
