United Nations Secretary-General Ban Ki-moon warned on Tuesday that a solely military response to the threat of Islamic State in Syria could fuel the radicalization of more Sunni armed groups and spark more violence.

"Our long-term strategic objective in Syria remains a political solution," Ban told the U.N. Security Council of efforts to end Syria's three-and-a-half year civil war.

"A purely military response to the vicious new threat posed by (Islamic State) could ultimately contribute to the radicalization of other Sunni armed groups and spark a cycle of renewed violence," he said.

Islamic State has seized swathes of territory in Iraq and Syria and is being targeted by U.S.-led air strikes in both countries. The group has been crucifying and beheading prisoners and ordering non-Muslims and Shi'ites to convert or die.

The Sunni militant group is battling Kurdish forces for control of the Syrian town of Kobani at the Turkish border. U.N. envoy Staffan de Mistura, appointed by Ban to mediate a political solution in Syria to end the war, has warned thousands of people could be massacred if Kobani falls to Islamic State.

"Kobani is just one of many places across Syria where civilians are under imminent threat," Ban told the council meeting on the Middle East.

"In addition to the barbarity of (Islamic State), the Syrian government continues to brutally and indiscriminately attack populated areas including with barrel bombs," he said.

Ban urged the Security Council to fully support the efforts of de Mistura to "reduce the suffering of the Syrian people and contribute to a political solution." Some 3.2 million Syrians have fled the violence that has killed nearly 200,000 people since 2011, according to the United Nations.