At least 20 people have been killed and dozens injured in an explosion at a mosque during Friday prayers in Pakistan's capital, Islamabad, according to local officials. The blast at the Shiite mosque in the Tarlai area of the city prompted an emergency to be declared at three hospitals, with officials providing estimates of the injured ranging from 80 to over 100. The cause of the blast remains unclear, but reports suggest it may have been the work of a suicide bomber. Pakistan's Prime Minister, Shehbaz Sharif, has condemned the incident, expressing 'deep grief' over the loss of lives. This is a developing story and updates will follow.