Afghanistan: 'Surrender is not an option'

Fighters from a militant Islamic group in Afghanistan, allied to the Taleban, have told the BBC that they are considering joining forces with Islamic State, formerly known as ISIS - and will continue to fight against the Afghan government, even after NATO forces leave Afghanistan at the end of the year.

The fighters, from Hezb-e-Islami, told the BBC's World Affairs Editor John Simpson that they had links with some IS members, and prayed for them as great Islamic warriors.

They said they rejected Afghanistan's US-made constitution and would keep fighting until Sharia Law was established not just in Afghanistan, but throughout the world.

John Simpson asked Afghanistan's former intelligence chief, Amrullah Saleh - for many years the head of the Directorate of National Security - whether he was worried that IS could link up with the Taleban or other militant Islamic groups in Afghanistan.