A US-born spokesman for al-Qaeda has been arrested in Karachi, Pakistani security officials have said.

Adam Gadahn has appeared in a number of al-Qaeda videos, going back at least six years, encouraging violent jihad.

The latest emerged on Sunday - the same day as his arrest was reported - urging US Muslims to attack their own country.

He was charged with treason in the US in 2006 and a reward offered for his arrest - which has not yet been confirmed by Islamabad or Washington. ...