Mohammed Emwazi, also known as Jihadi John, was one of the most dreaded Islamic State terrorists in the world.
They have arrested a number of Islamic militants suspected of staging attacks to expand Islamic State influence in the country neighboring Syria.
The U.S. military says an opposition force of 12,000 to 15,000 is needed to retake the east from Islamic State.
For authorities struggling to prevent young Muslims from joining the wars in Syria and Iraq, understanding what drives these men is key.
Still, the US and Turkey are not in sync about Syria, and Biden's visit follows weeks of misunderstandings and harsh rhetoric emanating from both capitals.
Islamic State had sought to make a symbol out of Kobane by defeating the Kurdish forces seeking to retain control of the town.
European jihadis have taken an increasingly visible role in propaganda by the Islamic State group, as the militants try to demonstrate a global profile.
Hundreds of young men from Western nations have travelled to Syria and Iraq to join Islamic State fighters who have seized swathes of those two countries.
The Syrian military widely uses so-called "barrel bombs" to strike at rebel-held areas.
Islamic State also holds large sections of territory elsewhere in the wider Aleppo province.
The video marked a new high in staged brutality by what is considered the most violent group in modern jihad, but some analysts see it as Islamic State's nervousness.
Below is a list of executions of Westerners this year by militants or movements linked to the jihadist Islamic State group:
The disclosure came hours after a father in Britain said he believed his son, a British medical student, was in the Islamic State squad filmed beheading the soldiers.
Nasser Muthana had already appeared in a online video released in June urging Muslims to join Islamic State.
The video emerged just minutes after President Barack Obama departed Australia for the US The president was in Australia for the Group of 20 economic summit.
Kassig had been in the region since March 2012, when he traveled to Lebanon on a break from university.
The same video showed the gruesome simultaneous beheadings of at least 18 men described as Syrian military personnel by Islamic State.
Kassig, 26, was captured last year while helping provide medical aid to Syrians. His friends say he converted to Islam in captivity and changed his name to Abdul-Rahman.
A new video featuring John Cantlie, a British photojournalist captured almost two years ago by Islamic State in Syria, reading messages has been released.
A masked Islamic State militant seen wielding a knife in videos at the beheading of two Americans has been identified, FBI said.