Among the dead were two policemen, he said.
The Pakistani Taliban has confirmed the death of the son of leader Mullah Fazlullah in a suspected US drone strike on March 6. In late January, a Taliban attacker drove an ambulance filled with explosives into the heart of the city, killing at least 103 people and wounding as many as 235.
The spokesman for the Health Ministry, Wahid Majro, said several of the wounded were in critical condition and feared the death toll could rise further.
Afghan President Ashraf Ghani at an global conference in Kabul last week unveiled a plan to open talks with the Taliban, including eventually recognising them as a political party.
"We were inside the mosque when a loud explosion took place".
On February 28, Ghani offered to allow the Taliban to establish itself as a political party and said he would work to remove sanctions on the militant group, among other incentives, if it joined the government in peace negotiations.
In northern Afghanistan, the Taliban attacked an army outpost overnight in an hourslong firefight and ambushed policemen sent to help the troops, killing six soldiers and 10 policemen. Mazari was killed by the Taliban in 1995.
In return, Ghani said the militants should officially recognize the Afghan government and constitution, a perennial sticking point in past attempts at dialogue.
Tadamichi Yamamoto told the Security Council Thursday the Taliban's argument that it won't talk to the government because the conflict is not between Afghan parties "misrepresents the reality".
Fazlullah and his Taliban militants are part of ongoing frustration from the US and Kabul toward Pakistan's efforts to combat insurgents. "These attacks are a blow to the president's efforts to hold talks with the Taliban and a clear signal that they reject his offer".