The United Nations on Thursday warned about Islamist militant networks increasingly forging links across the border of Syria and Iraq, which is fueling sectarian tensions in a region that has suffered from years of bloodshed.

Violence in Iraq reached new highs in 2013, when nearly 8,000 civilians were killed. Its political elite remains deeply divided along sectarian lines, as it has been since after the U.S.-led invasion of Iraq 11 years ago this month.

“The ongoing conflict in Syria has added a regional dimension to sectarian tensions and is affording terrorist networks the occasion to forge links across the border and expand their support base,” U.N. special envoy to Iraq Nickolay Mladenov told the 15-nation Security Council.