Carter arrived in Afghanistan on Friday in a surprise visit after he spent the last two days in Iraq. The US defense secretary was planning to meet his country's military commanders and troops stationed in the Nangarhar province in eastern Afghanistan, Reuters news agency reported.

Carter's visit came after the top US commander in the region, Gen. John Campbell, raised doubts that foreign fighters from Syria and Iraq were joining Afghans who had declared loyalty to "Islamic State" (IS) militants fighting at Pakistan's border in Afghanistan's east. In an interview with the Associated Press, Campbell said IS supporters were trying to establish a regional base in the Afghan city of Jalalabad.

Pentagon report questions Afghan peace

Campbell's suspicions came shortly after the Pentagon released a report earlier this week, painting a grim picture of the security situation in Afghanistan. According to the report, from the beginning of the 2015 to mid-November, the number of casualties on Afghan forces had increased by 27 percent. The number of high-profile attacks on the troops had also increased by the same proportion, the report found.

Doubts regarding peace in Afghanistan have increased after the northern city Kunduz fell briefly into the hands of the Taliban in September and a raid on Kandahar's airport last week that killed 50 civilians.

Around 9,800 US troops are stationed in Afghanistan. Their mission includes training and advising Afghan soldiers as well as conducting counterterrorism operations. In October, US President Barack Obama reversed his policy on the country to extend his troops' stay to the end of 2016.

On Thursday, the German parliament also approved a motion to extend its Afghan mission to the end of 2016.

mg/sms (Reuters, AP)