The wounded were rushed to hospital after the blast. (Photo: AFP)
At least 17 people have been killed and 37 wounded in an explosion at a mosque in the Afghan province of Khost, local officials say.
People had gathered for afternoon prayers at the mosque, which was also being used as a voter registration centre.
Some of the injured are said to be in a critical condition.
No group has claimed responsibility but the Islamic State group has carried out similar attacks in the past.
The latest incident appears to have been caused by explosives left in the mosque, rather than by a suicide bomber.
There have been a number of attacks on voter registration centres since the process started last month for October's parliamentary elections.
On 22 April, a suicide bomb attack at a voter registration centre in the capital Kabul killed at least 57 people.
The Kabul attack was claimed by IS, but the Taliban has also warned people not to take part in the elections, which are said to be a key test of President Ashraf Ghani's credibility.
In another development, police in the province of Baghlan say that seven Indian engineers and their Afghan driver, working for an electricity provider, were kidnapped by the Taliban on Sunday morning.
A police spokesman, Zabihullah Shuja, told the BBC that they were travelling to a government-run power station in Pul-e Khomri, the capital of the northern province.