A suicide bomber kills 15 Afghan army trainees as they travel home from their base in Kabul, officials say, as militants intensify a deadly rampage that has claimed more than 200 lives this week.

A US air strike that destroyed a medical charity's clinic in northern Afghanistan, killing 42 people, was not a war crime, the Pentagon has said.

US President Barack Obama apologises to the president of aid agency Medecins San Frontieres (MSF) for a bombing that killed at least 22 in the Afghan city of Kunduz.