Pentagon chief in Afghanistan as violence escalates

US Defense Secretary Ashton Carter arrived in Afghanistan Friday for meetings with military commanders, as the security situation deteriorates with a surge in Taliban attacks and the creeping emergence of the Islamic State group.

The unannounced visit comes just days after a Pentagon report presented a grim portrait of the war which has inflicted a growing number of casualties on hard-pressed Afghan forces.

During an event with soldiers at a US base near Jalalabad city in the eastern province of Nangarhar, Secretary Carter warned of the Taliban's continued threat to security in the country, while lauding the troops for training Afghan forces to battle the insurgents.

"The Afghan security forces are getting there," said Carter, according to a statement released by the Department of Defense.

"They're fighting, number one, and number two, they're fighting more and more effectively as they operate more and more on their own."

The volatile province of Nangarhar also faces an emerging threat from loyalists of the Islamic State group (IS), which is making gradual inroads in Afghanistan, challenging the Taliban on their own turf.

During his speech, Carter vowed to root out IS in both the Middle East and elsewhere. 

"We're going to kill it in its home tumour of Iraq and Syria," said Carter. "But then we have to recognise that there are little nests of it spring up all over all over the world."

This month marks a year since the US and NATO-led mission in Afghanistan transitioned into an Afghan-led operation, with allied nations assisting in training local forces.

President Barack Obama in October announced that thousands of US troops will remain in Afghanistan past 2016, backpedalling on previous plans to shrink the force and acknowledging that Afghan forces are not ready to stand alone.

The Taliban briefly captured the strategic northern city of Kunduz in September in their most spectacular victory in 14 years, dealing a stinging blow to Afghan forces as they battle the insurgents on multiple fronts.

The Taliban have since then threatened several other provincial centres from Lashkar Gah in the south to Maimana in the northwest raising concerns that Afghanistan was on the brink of a security collapse.