Hyder said the blast appeared to have been caused by a lone suicide bomber.
"The attack took place in a village near the border with Swat, in a mosque which takes care of about 250 families that have settled in that particular area," he reported.
Hyder said that the assailants blocked the roads from the mosque, preventing the wounded from being taken to hospital.
"It must be remembered that in Lower Dir the Pakistan military has been on the offensive [against the Taliban], and the government has been making no secret of the fact that there are elements trying to destabilise Pakistan.
"When this operation started it was expected that there would be very still resistance from the Pakistani Taliban.
"The military was able to overwhelm those militants ... but while the military has been moving on the ground they need the support of the civilian elements."
The latest blast is the ninth bomb attack in the country since the army launched a major offensive against the Taliban in neighbouring Swat valley.
The operation is aimed at flushing out Taliban fighters from the region.
Richard Holbrooke, the US special envoy to Afghanistan and Pakistan, was in Islamabad on Friday to consult the country's leaders on what needs to be done after confronting the Taliban in the Swat valley.
Elsewhere, a member of Pakistan's parliament and his family were wounded on Friday when a parcel bomb exploded at his home in the southern city of Karachi, police said.